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Typhoons exert significant but differential impacts on net ecosystem carbon exchange of subtropical mangrove forests in ChinaBiogeosciences, 11, 5323-5333, 2014Author(s): H. Chen, W. Lu, G. Yan, S. Yang, and G. LinTyphoons are very unpredictable natural disturbances to subtropical mangrove
forests in Asian countries, but little information is available on how these
disturbances affect ecosystem level carbon dioxide (CO2) exchange of
mangrove wetlands. In this study, we examined short-term effect of frequent
strong typhoons on defoliation and net ecosystem CO2 exchange (NEE) of
subtropical mangroves, and also synthesized 19 typhoons during a 4-year
period between 2009 and 2012 to further investigate the regulation
mechanisms of typhoons on ecosystem carbon and water fluxes following
typhoon disturbances. Strong wind and intensive rainfall caused defoliation
and local cooling effect during the typhoon season. Daily total NEE values
decreased by 26–50% following some typhoons (e.g., W28-Nockten,
W35-Molave and W35-Lio-Fan), but significantly increased (43–131%)
following typhoon W23-Babj and W38-Megi. The magnitudes and trends of daily
NEE responses were highly variable following different typhoons, which were
determined by the balance between the variances of gross ecosystem
production (GEP) and ecosystem respiration (RE). Furthermore, results from
our synthesis indicated that the landfall time of typhoon, wind speed and
rainfall were the most important factors controlling the CO2 fluxes
following typhoon events. These findings indicate that different types of
typhoon disturbances can exert very different effects on CO2 fluxes of
mangrove ecosystems and that typhoon will likely have larger impacts on
carbon cycle processes in subtropical mangrove ecosystems as the intensity
and frequency of typhoons are predicted to increase under future global
climate change scenarios. 2014/10/02 - 17:24

Speciation and dynamics of dissolved inorganic nitrogen export in the Danshui River, TaiwanBiogeosciences, 11, 5307-5321, 2014Author(s): T.-Y. Lee, Y.-T. Shih, J.-C. Huang, S.-J. Kao, F.-K. Shiah, and K.-K. LiuHuman-induced excess nitrogen outflowing from land through rivers to oceans
has resulted in serious impacts on terrestrial and coastal ecosystems.
Oceania, which occupies < 2.5% of the global land surface, delivers
12% of the freshwater and dissolved materials to the ocean on a global
scale. However, there are few empirical data sets on riverine dissolved
inorganic nitrogen (DIN) fluxes in the region, and their dynamics are poorly
understood. In this study, a river monitoring network covering different
types of land uses and population densities was implemented to investigate
the mechanism of DIN export. The results show that DIN concentration/yield
varied from
∼20 μM/∼300 kg-N km−2 yr−1 to
∼378 μM/∼10 000 kg-N km−2 yr−1
from the relatively pristine headwaters to the populous estuary. Agriculture
and population density control DIN export in less densely populated regions
and urban areas, respectively, and runoff controls DIN at the watershed
scale. Compared to documented estimates from global models, the observed DIN
export from the Danshui River is 2.3 times larger, which results from the
region-specific response of DIN yield to dense population and abundant
runoff. The dominating DIN species change gradually from NO3− in the
headwaters (∼97%) to NH4+ in the estuary
(∼60%) following the urbanization gradient. The prominent
existence of NH4+ is probably the result of the anaerobic water body
and short residence time, unlike in large river basins. Given the analogous
watershed characteristics of the Danshui River to the rivers in Oceania, our
study could serve as a first example to examine riverine DIN fluxes in
Oceania. 2014/10/02 - 17:24

Mechanisms of microbial carbon sequestration in the ocean – future research directionsBiogeosciences, 11, 5285-5306, 2014Author(s): N. Jiao, C. Robinson, F. Azam, H. Thomas, F. Baltar, H. Dang, N. J. Hardman-Mountford, M. Johnson, D. L. Kirchman, B. P. Koch, L. Legendre, C. Li, J. Liu, T. Luo, Y.-W. Luo, A. Mitra, A. Romanou, K. Tang, X. Wang, C. Zhang, and R. ZhangThis paper reviews progress on understanding biological carbon sequestration
in the ocean with special reference to the microbial formation and
transformation of recalcitrant dissolved organic carbon (RDOC), the
microbial carbon pump (MCP). We propose that RDOC is a concept with a wide
continuum of recalcitrance. Most RDOC compounds maintain their levels of
recalcitrance only in a specific environmental context (RDOCt). The
ocean RDOC pool also contains compounds that may be inaccessible to microbes
due to their extremely low concentration (RDOCc). This differentiation
allows us to appreciate the linkage between microbial source and RDOC
composition on a range of temporal and spatial scales.

Analyses of biomarkers and isotopic records show intensive MCP processes in
the Proterozoic oceans when the MCP could have played a significant role in
regulating climate. Understanding the dynamics of the MCP in conjunction
with the better constrained biological pump (BP) over geological timescales
could help to predict future climate trends. Integration of the MCP and the
BP will require new research approaches and opportunities. Major goals
include understanding the interactions between particulate organic carbon
(POC) and RDOC that contribute to sequestration efficiency, and the
concurrent determination of the chemical composition of organic carbon,
microbial community composition and enzymatic activity. Molecular biomarkers
and isotopic tracers should be employed to link water column processes to
sediment records, as well as to link present-day observations to
paleo-evolution. Ecosystem models need to be developed based on empirical
relationships derived from bioassay experiments and field investigations in
order to predict the dynamics of carbon cycling along the stability
continuum of POC and RDOC under potential global change scenarios. We
propose that inorganic nutrient input to coastal waters may reduce the
capacity for carbon sequestration as RDOC. The nutrient regime enabling
maximum carbon storage from combined POC flux and RDOC formation should
therefore be sought. 2014/10/02 - 17:24

Declining ozone exposure of European vegetation under climate change and reduced precursor emissionsBiogeosciences, 11, 5269-5283, 2014Author(s): J. Klingberg, M. Engardt, P. E. Karlsson, J. Langner, and H. PleijelThe impacts of changes in ozone precursor emissions as well as climate
change on the future ozone exposure of the vegetation in Europe were
investigated. The ozone exposure is expressed as AOT40 (Accumulated
exposure Over a Threshold of 40 ppb O3) as well as PODY
(Phytotoxic Ozone Dose above a threshold Y). A new method is
suggested to express how the length of the period during the year when
coniferous and evergreen trees are sensitive to ozone might be affected by
climate change. Ozone precursor emission changes from the RCP4.5 scenario
were combined with climate simulations based on the IPCC SRES A1B scenario
and used as input to the Eulerian Chemistry Transport Model MATCH from which
projections of ozone concentrations were derived. The ozone exposure of
vegetation over Europe expressed as AOT40 was projected to be substantially
reduced between the periods 1990–2009 and 2040–2059 to levels which are well
below critical levels used for vegetation in the EU directive 2008/50/EC as
well as for crops and forests used in the LRTAP convention, despite that the
future climate resulted in prolonged yearly ozone sensitive periods. The
reduction in AOT40 was mainly driven by the emission reductions, not changes
in the climate. For the toxicologically more relevant POD1 index the
projected reductions were smaller, but still significant. The values for
POD1 for the time period 2040–2059 were not projected to decrease to
levels which are below critical levels for forest trees, represented by
Norway spruce. This study shows that substantial reductions of ozone
precursor emissions have the potential to strongly reduce the future risk
for ozone effects on the European vegetation, even if concurrent climate
change promotes ozone formation. 2014/10/02 - 17:24

X-ray fluorescence mapping of mercury on suspended mineral particles and diatoms in a contaminated freshwater systemBiogeosciences, 11, 5259-5267, 2014Author(s): B. Gu, B. Mishra, C. Miller, W. Wang, B. Lai, S. C. Brooks, K. M. Kemner, and L. LiangMercury (Hg) bioavailability and geochemical cycling is affected by its
partitioning between the aqueous and particulate phases. We applied a
synchrotron-based X-ray fluorescence (XRF) microprobe to visualize and
quantify directly the spatial localization of Hg and its correlations with
other elements of interest on suspended particles from a Hg-contaminated
freshwater system. Up to 175 μg g−1 Hg is found on suspended
particles, but less than 0.01% is in the form of methylmercury. Mercury
is heterogeneously distributed among phytoplankton (e.g., diatoms) and
mineral particles that are rich in iron oxides and natural organic matter
(NOM). The diatom-bound Hg is mostly found on outer surfaces of the cells,
suggesting passive sorption of Hg on diatoms. Our results indicate that
localized sorption of Hg onto suspended particles, including diatoms and
NOM-coated oxide minerals, may play an important role in affecting the
partitioning, reactivity, and biogeochemical cycling of Hg in natural aquatic
environments. 2014/10/02 - 17:24

Methane and nitrous oxide sources and emissions in a subtropical freshwater reservoir, South East Queensland, AustraliaBiogeosciences, 11, 5245-5258, 2014Author(s): K. Sturm, Z. Yuan, B. Gibbes, U. Werner, and A. GrinhamReservoirs have been identified as an important source of non-carbon dioxide
(CO2) greenhouse gases with wide ranging fluxes for reported methane
(CH4); however, fluxes for nitrous oxide (N2O) are rarely
quantified. This study investigates CH4 and N2O sources and
emissions in a subtropical freshwater Gold Creek Reservoir, Australia,
using a combination of water–air and sediment–water flux measurements and
water column and pore water analyses. The reservoir was clearly a source of
these gases as surface waters were supersaturated with CH4 and N2O.
Atmospheric CH4 fluxes were dominated by ebullition (60 to 99%)
relative to diffusive fluxes and ranged from 4.14 × 102 to
3.06 × 105 μmol CH4 m−2 day−1 across
the sampling sites. Dissolved CH4 concentrations were highest in the
anoxic water column and sediment pore waters (approximately 5 000 000%
supersaturated). CH4 production rates of up to
3616 ± 395 μmol CH4 m−2 day−1 were found
during sediment incubations in anoxic conditions. These findings are in
contrast to N2O where no production was detected during sediment
incubations and the highest dissolved N2O concentrations were found in
the oxic water column which was 110 to 220% supersaturated with
N2O. N2O fluxes to the atmosphere were primarily through the
diffusive pathway, mainly driven by diffusive fluxes from the water column
and by a minor contribution from sediment diffusion and ebullition. Results
suggest that future studies of subtropical reservoirs should monitor CH4
fluxes with an appropriate spatial resolution to ensure capture of ebullition
zones, whereas assessment of N2O fluxes should focus on the diffusive
pathway. 2014/10/02 - 17:24

Australian net (1950s–1990) soil organic carbon erosion: implications for CO2 emission and land–atmosphere modellingBiogeosciences, 11, 5235-5244, 2014Author(s): A. Chappell, N. P. Webb, R. A. Viscarra Rossel, and E. BuiThe debate remains unresolved about soil erosion substantially offsetting fossil fuel emissions
and acting as an important source or sink of CO2.
There is little historical land use and management context to this debate,
which is central to Australia's recent past of European settlement,
agricultural expansion and agriculturally-induced soil erosion. We use
"catchment" scale (∼25 km2) estimates of 137Cs-derived
net (1950s–1990) soil redistribution of all processes (wind, water and
tillage) to calculate the net soil organic carbon (SOC) redistribution across
Australia. We approximate the selective removal of SOC at net eroding
locations and SOC enrichment of transported sediment and net depositional
locations. We map net (1950s–1990) SOC redistribution across Australia and
estimate erosion by all processes to be ∼4 Tg SOC yr−1, which
represents a loss of ∼2% of the total carbon stock (0–10 cm) of
Australia. Assuming this net SOC loss is mineralised, the flux
(∼15 Tg CO2-equivalents yr−1) represents an omitted 12% of
CO2-equivalent emissions from all carbon pools in Australia. Although a small
source of uncertainty in the Australian carbon budget, the mass flux
interacts with energy and water fluxes, and its omission from land surface
models likely creates more uncertainty than has been previously recognised. 2014/10/02 - 17:24

Genotyping an Emiliania huxleyi (prymnesiophyceae) bloom event in the North Sea reveals evidence of asexual reproductionBiogeosciences, 11, 5215-5234, 2014Author(s): S. A. Krueger-Hadfield, C. Balestreri, J. Schroeder, A. Highfield, P. Helaouët, J. Allum, R. Moate, K. T. Lohbeck, P. I. Miller, U. Riebesell, T. B. H. Reusch, R. E. M. Rickaby, J. Young, G. Hallegraeff, C. Brownlee, and D. C. SchroederDue to the unprecedented rate at which our climate is changing, the ultimate
consequence for many species is likely to be either extinction or migration
to an alternate habitat. Certain species might, however, evolve at a rate
that could make them resilient to the effects of a rapidly changing
environment. This scenario is most likely to apply to species that have large
population sizes and rapid generation times, such that the genetic variation
required for adaptive evolution can be readily supplied. Emiliania
huxleyi (Lohm.) Hay and Mohler (Prymnesiophyceae) is likely to be such a
species, as it is the most conspicuous extant calcareous phytoplankton species
in our oceans with growth rates of 1 day−1. Here we report on a
validated set of microsatellites, in conjunction with the coccolithophore
morphology motif genetic marker, to genotype 93 clonal isolates collected
from across the world. Of these, 52 came from a single bloom event in the
North Sea collected on the D366 United Kingdom Ocean Acidification cruise in
June–July 2011. There were 26 multilocus genotypes (MLGs) encountered only
once in the North Sea bloom and 8 MLGs encountered twice or up to six times.
Each of these repeated MLGs exhibited Psex values of less than
0.05, indicating each repeated MLG was the product of asexual reproduction and
not separate meiotic events. In addition, we show that the two most
polymorphic microsatellite loci, EHMS37 and P01E05, are reporting on regions
likely undergoing rapid genetic drift during asexual reproduction. Despite
the small sample size, there were many more repeated genotypes than
previously reported for other bloom-forming phytoplankton species, including
a previously genotyped E. huxleyi bloom event. This study
challenges the current assumption that sexual reproduction predominates
during bloom events. Whilst genetic diversity is high amongst extant
populations of E. huxleyi, the root cause for this diversity and
ultimate fate of these populations still requires further examination.
Nonetheless, we show that certain CMM genotypes are found everywhere, while
others appear to have a regional bias. 2014/10/02 - 17:24

Carbon losses from pyrolysed and original wood in a forest soil under natural and increased N depositionBiogeosciences, 11, 5199-5213, 2014Author(s): B. Maestrini, S. Abiven, N. Singh, J. Bird, M. S. Torn, and M. W. I. SchmidtPyrogenic organic matter (PyOM) plays an important role as a stable carbon
(C) sink in the soils of terrestrial ecosystems. However, uncertainties
remain about in situ turnover rates of fire-derived PyOM in soil, the main
processes leading to PyOM-C and nitrogen (N) losses from the soil, and the
role of N availability on PyOM cycling in soils.

We measured PyOM and native soil organic carbon losses from the soil as
carbon dioxide and dissolved organic carbon (DOC) using additions of highly
13C-labelled PyOM (2.03 atom %) and its precursor pinewood during
1 year in a temperate forest soil. The field experiment was
carried out under ambient and increased mineral N deposition (+60 kg
N-NH4NO3 ha−1 year−1). The results showed that after 1 year: (1) 0.5% of PyOM-C and 22% of wood-C were mineralized as
CO2, leading to an estimated turnover time of 191 and 4 years,
respectively; (2) the quantity of PyOM and wood lost as dissolved organic
carbon was negligible (0.0004 ± 0.0003% and 0.022 ± 0.007% of applied-C, respectively); and (3) N additions decreased cumulative
PyOM mineralization by 43%, but did not affect cumulative wood
mineralization and did not affect the loss of DOC from PyOM or wood. We
conclude that mineralization to CO2 was the main process leading to PyOM
losses during the first year of mineralization in a forest soil, and that N
addition can decrease PyOM-C cycling, while added N showed no effect on wood
C cycling. 2014/10/02 - 17:24

Land surface phenological response to decadal climate variability across Australia using satellite remote sensingBiogeosciences, 11, 5181-5198, 2014Author(s): M. Broich, A. Huete, M. G. Tulbure, X. Ma, Q. Xin, M. Paget, N. Restrepo-Coupe, K. Davies, R. Devadas, and A. HeldLand surface phenological cycles of vegetation greening and browning are
influenced by variability in climatic forcing. Quantitative spatial
information on phenological cycles and their variability is important for
agricultural applications, wildfire fuel accumulation, land management, land
surface modeling, and climate change studies. Most phenology studies have
focused on temperature-driven Northern Hemisphere systems, where phenology
shows annually recurring patterns. However, precipitation-driven non-annual
phenology of arid and semi-arid systems (i.e., drylands) received much less
attention, despite the fact that they cover more than 30% of the global
land surface. Here, we focused on Australia, a continent with one of the most
variable rainfall climates in the world and vast areas of dryland systems,
where a detailed phenological investigation and a characterization of the
relationship between phenology and climate variability are missing.

To fill this knowledge gap, we developed an algorithm to characterize
phenological cycles, and analyzed geographic and climate-driven variability
in phenology from 2000 to 2013, which included extreme drought and wet years.
We linked derived phenological metrics to rainfall and the Southern
Oscillation Index (SOI). We conducted a continent-wide investigation and a
more detailed investigation over the Murray–Darling Basin (MDB), the primary
agricultural area and largest river catchment of Australia.

Results showed high inter- and intra-annual variability in phenological
cycles across Australia. The peak of phenological cycles occurred not only
during the austral summer, but also at any time of the year, and their timing
varied by more than a month in the interior of the continent. The magnitude
of the phenological cycle peak and the integrated greenness were most
significantly correlated with monthly SOI within the preceding 12 months.
Correlation patterns occurred primarily over northeastern Australia and
within the MDB, predominantly over natural land cover and particularly in
floodplain and wetland areas. Integrated greenness of the phenological cycles
(surrogate of vegetation productivity) showed positive anomalies of more than
2 standard deviations over most of eastern Australia in 2009–2010, which
coincided with the transition from the El Niño-induced decadal droughts
to flooding caused by La Niña. 2014/10/02 - 17:24

Evidence for vivianite formation and its contribution to long-term phosphorus retention in a recent lake sediment: a novel analytical approachBiogeosciences, 11, 5169-5180, 2014Author(s): M. Rothe, T. Frederichs, M. Eder, A. Kleeberg, and M. HupferVivianite, Fe3(PO4)2 · 8 H2O, is a ferrous iron
phosphate mineral which forms in waterlogged soils and
sediments. The phosphorus (P) bound in its crystal lattice is
considered to be immobilised because vivianite is stable under
anoxic, reducing, sedimentary conditions. Thus, vivianite formation
can make a major contribution to P retention during early
diagenesis. Much remains unknown about vivianite in sediments,
because technical challenges have rendered direct identification and
quantification difficult. To identify vivianite and assess its
significance for P burial during early diagenesis we studied the
consequences of a 1992/1993 in-lake application of FeCl3 and
Fe(OH)3 aimed at restoring Lake Groß-Glienicke (Berlin,
Germany). In a novel approach, we firstly applied a heavy-liquid
separation to the iron-rich surface sediments which allowed direct
identification of vivianite by X-ray diffraction in the high-density
(ρ > 2.3 g cm−3) sediment fraction. Secondly, we
assessed the contribution of vivianite to P retention, combining
results from chemical digestion with magnetic susceptibility data
derived from magnetic hysteresis measurements. Scanning electron
microscopy revealed that the dark blue spherical vivianite nodules
were 40–180 μm in diameter, and formed of platy- and
needle-shaped crystal aggregates. Although equilibrium calculations
indicated supersaturation of vivianite throughout the upper
30 cm of the sediment, the vivianite deposits were
homogeneously distributed within, and restricted to, the upper
23 cm only. Thus, supersaturated pore water alone cannot
serve as a reliable predictor for the in situ formation of
vivianite. In Lake Groß -Glienicke, vivianite formation continues
to be triggered by the artificial iron amendment more than
20 yr ago, significantly contributing to P retention in
surface sediments. 2014/09/27 - 10:08

Modern and Cenozoic records of seawater magnesium from foraminiferal Mg isotopesBiogeosciences, 11, 5155-5168, 2014Author(s): P. A. E. Pogge von Strandmann, J. Forshaw, and D. N. SchmidtMagnesium is an element critically involved in the carbon cycle, because
weathering of Ca-Mg silicates removes atmospheric CO2 into rivers, and
formation of Ca-Mg carbonates in the oceans removes carbon from the
ocean-atmosphere system. Hence the Mg cycle holds the potential to provide
valuable insights into Cenozoic climate-system history, and the shift during
this time from a greenhouse to icehouse state. We present Mg isotope ratios
for the past 40 Myr using planktic foraminifers as an archive. Modern
foraminifera, which discriminate against elemental and isotopically heavy Mg
during calcification, show no correlation between the Mg isotope composition
(δ26Mg, relative to DSM-3) and temperature, Mg / Ca or other
parameters such as carbonate saturation (ΔCO3). However,
inter-species isotopic differences imply that only well-calibrated single
species should be used for reconstruction of past seawater. Seawater δ26Mg inferred from the foraminiferal record decreased from
~0‰ at 15 Ma, to
−0.83‰ at the present day, which coincides with
increases in seawater lithium and oxygen isotope ratios. It strongly
suggests that neither Mg concentrations nor isotope ratios are at
steady state in modern oceans, given its ~10 Myr residence
time. From these data, we have developed a dynamic box model to understand
and constrain changes in Mg sources to the oceans (rivers) and Mg sinks
(dolomitisation and hydrothermal alteration). Our estimates of seawater Mg
concentrations through time are similar to those independently determined by
pore waters and fluid inclusions. Modelling suggests that dolomite formation
and the riverine Mg flux are the primary controls on the δ26Mg
of seawater, while hydrothermal Mg removal and the δ26Mg of
rivers are more minor controls. Using Mg riverine flux and isotope ratios
inferred from the 87Sr / 86Sr record, the modelled Mg removal by
dolomite formation shows minima in the Oligocene and at the present day
(with decreasing trends from 15 Ma), both coinciding with rapid decreases in
global temperatures. 2014/09/27 - 10:08

The impact of climate variation and disturbances on the carbon balance of forests in Hokkaido, JapanBiogeosciences, 11, 5139-5154, 2014Author(s): R. Hirata, K. Takagi, A. Ito, T. Hirano, and N. SaigusaWe evaluated the long-term (52-year) effect of climate, disturbance, and
subsequent recovery on the carbon balance of cool temperate forests by using
the process-based ecosystem model VISIT. The study sites were artificial
larch forests planted after clear-cutting of mixed forest in Hokkaido, Japan.
The model was validated, scenarios were computed, and a sensitivity analysis
was performed. First, we performed a baseline simulation of carbon dynamics
and compared these values with those observed across a wide range of stand
ages (old mixed forest and young and middle-aged larch forests). Second, we
ran scenarios to investigate how disturbance and several climate factors
affect long-term carbon fluxes. Third, we analyzed the sensitivity of carbon
balance to the amount of disturbance-generated tree biomass residues. By
taking into account seasonal variation in the understory leaf area index,
which played an important role, especially in the initial stage of recovery,
the simulated net ecosystem production (NEP), gross primary production,
ecosystem respiration, and biomass for the three types of forest were
consistent with observed values (mean ± SD of R2 of monthly NEP,
GPP and RE for the three types of forest were 0.63 ± 0.26,
0.93 ± 0.07, 0.94 ± 0.2, respectively). The effect of
disturbances such as clear-cutting, land-use conversion, and thinning on the
long-term trend of NEP was larger than that of climate variation, even 50
years after clear-cutting. In contrast, interannual variation in the carbon
balance was primarily driven by climate variation. These findings indicate
that disturbance controlled the long-term trend of the carbon balance,
whereas climate factors controlled yearly variation in the carbon balance.
Among the meteorological factors considered, temperature and precipitation
were the main ones that affected NEP and its interannual variation. The
carbon balance in the initial post-disturbance period, which is strongly
affected by the amount of residues, influenced the subsequent long-term
carbon budget, implying the importance of residue management. Consequently,
carbon release just after disturbance and the length of the recovery period
required to balance the carbon budget are controlled by the amount of
residues. 2014/09/27 - 10:08

Spatial variability and the fate of cesium in coastal sediments near Fukushima, JapanBiogeosciences, 11, 5123-5137, 2014Author(s): E. E. Black and K. O. BuesselerQuantifying the amount of cesium incorporated into marine
sediments as a result of the Fukushima Dai-ichi Nuclear Power Plant (FDNPP)
accident has proven challenging due to the limited multi-core sampling from
within the 30 km zone around the facility; the inherent spatial
heterogeneities in ocean sediments; and the potential for inventory
fluctuations due to physical, biological, and chemical processes. Using
210Pb, 234Th, 137Cs, and 134Cs profiles from 20 sediment
cores, coastal sediment inventories were reevaluated. A 137Cs sediment
inventory of 100 ± 50 TBq was found for an area of 55 000 km2
using cores from this study and a total of 130 ± 60 TBq using an
additional 181 samples. These inventories represent less than 1% of the
estimated 15–30 PBq of cesium released during the FDNPP disaster. The time
needed for surface sediment activities (0 to 3 cm) at the 20 locations to be
reduced by 50% via sediment mixing was estimated to range from 0.4 to
26 yr. Due to the observed variability in mixing rates, grain size, and
inventories, additional cores are needed to improve these estimates and
capture the full extent of cesium penetration into the shallow coastal
sediments, which was deeper than 14 cm for all cores retrieved from water
depths less than 150 m. 2014/09/24 - 13:58

An experimental study on the effects of nutrient enrichment on organic carbon persistence in the western Pacific oligotrophic gyreBiogeosciences, 11, 5115-5122, 2014Author(s): J. Liu, N. Jiao, and K. TangCarbon sequestration in the ocean is of great concern with respect to the
mitigation of global warming. How to hold the fixed organic carbon in the
presence of tremendous numbers of heterotrophic microorganisms in marine
environments is the central issue. We previously hypothesized that excessive
nutrients would ultimately decrease the storage of organic carbon in marine
environments. To test this, a series of in situ nutrient enrichment
incubation experiments were conducted at a site (17.59° N,
127.00° E) within the western Pacific oligotrophic gyre. Five
treatments were employed: glucose (Glu), algal exudation organic material
(EOM), nitrate (N) and phosphate (P), N and P in combination with glucose and
a control with no added nutrients. The results showed that the dissolved
organic carbon consumption rates and bacterial community specific growth
rates were enhanced by inorganic nutrient enrichment treatments during the
initial 48 h incubation. At the end of 14 days of incubation, about
one-third (average 3.3 μmol C kg−1) more organic carbon was respired
in the glucose-enriched incubation with the addition of inorganic nutrients
compared to that without. In contrast, when nutrients were limiting, glucose
could not be efficiently used by the bacteria and thus it remained in the
environment. These results suggest that repletion of inorganic nutrients
could facilitate microbial consumption of organic carbon and thus has a
significant impact on carbon cycling in the environment. 2014/09/24 - 13:58

Soil organic matter dynamics under different land use in grasslands in Inner Mongolia (northern China)Biogeosciences, 11, 5103-5113, 2014Author(s): L. Zhao, W. Wu, X. Xu, and Y. XuWe examined bulk soil properties and molecular biomarker distributions in
surface soils from Inner Mongolian grasslands in order to understand the
responses of soil organic matter to different land use. A total of 16 soils
were collected from severely degraded grassland by overgrazing (DG), native
grassland without apparent anthropogenic disturbance (NG),
groundwater-sustaining grassland (GG) and restored grassland from previous
potato cropland (RG). Compared to NG, soil organic carbon content was lower
by 50% in DG, but higher by six-fold in GG and one-fold in RG. The
δ13C values of soil organic carbon were
–24.2 ± 0.6‰ in DG, –24.9 ± 0.6‰ in NG,
–25.1 ± 0.1‰ in RG and –26.2 ± 0.6‰ in GG,
reflecting different degradation degrees of soil organic matter or different
water use efficiencies. The soils in DG contained the lowest abundance of
aliphatic lipids (n-alkanes, n-alkanols, n-alkanoic acids, ω-hydroxylalkanoic acids and α-hydroxyalkanoic acids) and lignin-phenols, suggesting selective
removal of these biochemically recalcitrant biomarkers with grassland
degradation by microbial respiration or wind erosion. Compared to NG, the
soils in GG and RG increased ω-hydroxylalkanoic acids by
60–70%, a biomarker for suberin from roots, and increased α-hydroxylalkanoic acids by 10–20%, a biomarker for both cutin and
suberin. Our results demonstrate that the groundwater supply and
cultivation–restoration practices in Inner Mongolian grasslands not only
enhance soil organic carbon sequestration, but also change the proportions of
shoot- versus root-derived carbon in soils. This finding has important
implications for the global carbon cycle since root-derived aliphatic carbon
has a longer residence time than the aboveground tissue-derived carbon in
soils. 2014/09/24 - 13:58

Causal relationships versus emergent patterns in the global controls of fire frequencyBiogeosciences, 11, 5087-5101, 2014Author(s): I. Bistinas, S. P. Harrison, I. C. Prentice, and J. M. C. PereiraGlobal controls on month-by-month fractional burnt area (2000–2005) were
investigated by fitting a generalised linear model (GLM) to Global Fire
Emissions Database (GFED) data, with 11 predictor variables representing
vegetation, climate, land use and potential ignition sources. Burnt area is
shown to increase with annual net primary production (NPP), number of dry
days, maximum temperature, grazing-land area, grass/shrub cover and diurnal
temperature range, and to decrease with soil moisture, cropland area and
population density. Lightning showed an apparent (weak) negative influence,
but this disappeared when pure seasonal-cycle effects were taken into
account. The model predicts observed geographic and seasonal patterns, as
well as the emergent relationships seen when burnt area is plotted against
each variable separately. Unimodal relationships with mean annual temperature
and precipitation, population density and gross domestic product (GDP) are
reproduced too, and are thus shown to be secondary consequences of
correlations between different controls (e.g. high NPP with high
precipitation; low NPP with low population density and GDP). These findings
have major implications for the design of global fire models, as several
assumptions in current models – most notably, the widely assumed dependence
of fire frequency on ignition rates – are evidently incorrect. 2014/09/24 - 13:58

Trimethylamine emissions in animal husbandryBiogeosciences, 11, 5073-5085, 2014Author(s): J. Sintermann, S. Schallhart, M. Kajos, M. Jocher, A. Bracher, A. Münger, D. Johnson, A. Neftel, and T. RuuskanenDegradation of plant material by animals is an important transformation pathway in the nitrogen
(N) cycle. During the involved processes, volatile reduced alkaline nitrogen compounds, mainly
ammonia (NH3) and aliphatic amines such as trimethylamine (TMA), are formed. Today, animal
husbandry is estimated to constitute a main source of aliphatic amines in the atmosphere with
TMA being the main emitted compound. Here, we show how the interaction between faeces and urine in
animal production systems provides the primary source for agricultural TMA emissions. Excreted
urine contains large quantities of urea and TMA-N-oxide, which are transformed into NH3
and TMA, respectively, via enzymatic processes provided by microbes present in faeces. TMA
emissions from areas polluted with urine–faeces mixtures are on average of the order of 10 to
50 nmol m−2s−1. Released amines promote secondary aerosol particle formation in
the agricultural emission plume. The atmospheric lifetime of TMA, which was estimated to be of the order of 30 to 1000 s, is determined by the condensation onto aerosol particles. 2014/09/24 - 13:58

Updated estimates of carbon accumulation rates in coastal marsh sedimentsBiogeosciences, 11, 5057-5071, 2014Author(s): X. Ouyang and S. Y. LeeStudies on carbon stock in salt marsh sediments have increased since the
review by Chmura et al. (2003). However, uncertainties exist in estimating
global carbon storage in these vulnerable coastal habitats, thus hindering
the assessment of their importance. Combining direct data and indirect
estimation, this study compiled studies involving 143 sites across the
Southern and Northern hemispheres, and provides an updated estimate of the
global average carbon accumulation rate (CAR) at 244.7 g C m−2 yr−1
in salt marsh sediments. Based on region-specific CAR and estimates
of salt marsh area in various geographic regions between 40° S to
69.7° N, total CAR in global salt marsh sediments is estimated at
~10.2 Tg C yr−1. Latitude, tidal range and elevation
appear to be important drivers for CAR of salt marsh sediments, with
considerable variation among different biogeographic regions. The data
indicate that while the capacity for carbon sequestration by salt marsh
sediments ranked the first amongst coastal wetland and forested terrestrial
ecosystems, their carbon budget was the smallest due to their limited and
declining global areal extent. However, some uncertainties remain for our
global estimate owing to limited data availability. 2014/09/24 - 13:58

Contrasting patterns of litterfall seasonality and seasonal changes in litter decomposability in a tropical rainforest regionBiogeosciences, 11, 5047-5056, 2014Author(s): S. A. Parsons, V. Valdez-Ramirez, R. A. Congdon, and S. E. WilliamsThe seasonality of litter inputs in forests has important implications for
understanding ecosystem processes and biogeochemical cycles. We quantified
the drivers of seasonality in litterfall and leaf decomposability using plots
throughout the Australian wet tropical region. Litter fell mostly in the
summer (wet, warm) months in the region, but other peaks occurred throughout
the year. Litterfall seasonality was modelled well with the level of
deciduousness of the site (plots with more deciduous species had lower
seasonality than evergreen plots), temperature (higher seasonality in the
uplands), disturbance (lower seasonality with more early secondary species)
and soil fertility (higher seasonality with higher N : P/P
limitation) (SL total litterfall model 1 = deciduousness + soil
N : P + early secondary sp.: r2 = 0.63, n = 30; model
2 = temperature + early secondary sp. + soil N : P: r2 =
0.54, n = 30; SL leaf = temperature + early secondary
sp. + rainfall seasonality: r2 = 0.39, n = 30). Leaf litter
decomposability was lower in the dry season than in the wet season, driven by
higher phenolic concentrations in the dry, with the difference exacerbated
particularly by lower dry season moisture. Our results are contrary to the
global trend for tropical rainforests; in that seasonality of litterfall
input was generally higher in wetter, cooler, evergreen forests, compared to
generally drier, warmer, semi-deciduous sites that had more uniform monthly
inputs. We consider this due to more diverse litter shedding patterns in
semi-deciduous and raingreen rainforest sites, and an important consideration
for ecosystem modellers. Seasonal changes in litter quality are likely to
have impacts on decomposition and biogeochemical cycles in these forests due
to the litter that falls in the dry season being more recalcitrant to decay. 2014/09/24 - 13:58

Remotely sensed land-surface energy fluxes at sub-field scale in heterogeneous agricultural landscape and coniferous plantationBiogeosciences, 11, 5021-5046, 2014Author(s): R. Guzinski, H. Nieto, R. Jensen, and G. MendigurenIn this study we evaluate a methodology for disaggregating land surface
energy fluxes estimated with the Two-Source Energy Balance (TSEB)-based
Dual-Temperature Difference (DTD) model which uses day and night polar
orbiting satellite observations of land surface temperature (LST) as a
remotely sensed input. The DTD model is run with MODIS input data at
a spatial resolution of around 1 km while the disaggregation uses Landsat
observations to produce fluxes at a nominal spatial resolution of 30 m. The
higher-resolution modelled fluxes can be directly compared against eddy
covariance (EC)-based flux tower measurements to ensure more accurate model
validation and also provide a better visualization of the fluxes' spatial
patterns in heterogeneous areas allowing for development of, for example,
more efficient irrigation practices. The disaggregation technique is
evaluated in an area covered by the Danish Hydrological Observatory (HOBE),
in the west of the Jutland peninsula, and the modelled fluxes are compared
against measurements from two flux towers: the first one in a heterogeneous
agricultural landscape and the second one in a homogeneous conifer
plantation. The results indicate that the coarse-resolution DTD fluxes
disaggregated at Landsat scale have greatly improved accuracy as compared to
high-resolution fluxes derived directly with Landsat data without the
disaggregation. At the agricultural site the disaggregated fluxes display
small bias and very high correlation (r ≈ 0.95) with EC-based
measurements, while at the plantation site the results are encouraging but
still with significant errors. In addition, we introduce a~modification to
the DTD model by replacing the "parallel" configuration of the resistances
to sensible heat exchange by the "series" configuration. The latter takes
into account the in-canopy air temperature and substantially improves the
accuracy of the DTD model. 2014/09/24 - 13:58

Insights into oxygen transport and net community production in sea ice from oxygen, nitrogen and argon concentrationsBiogeosciences, 11, 5007-5020, 2014Author(s): J. Zhou, B. Delille, F. Brabant, and J.-L. TisonWe present and compare the dynamics (i.e., changes in standing stocks,
saturation levels and concentrations) of O2, Ar and N2 in landfast
sea ice, collected in Barrow (Alaska), from February through June 2009. The
comparison suggests that the dynamic of O2 in sea ice strongly depends
on physical processes (gas incorporation and subsequent transport). Since Ar
and N2 are only sensitive to the physical processes in the present
study, we then discuss the use of O2 / Ar and O2 / N2 to
correct for the physical contribution to O2 supersaturations, and to
determine the net community production (NCP). We conclude that O2 / Ar
suits better than O2 / N2, due to the relative abundance of O2,
N2 and Ar, and the lower biases when gas bubble formation and gas
diffusion are maximized. We further estimate NCP in the impermeable layers
during ice growth, which ranged from −6.6 to 3.6 μmol O2 L−1 d−1,
and the concentrations of O2 due to biological activity in the permeable layers
during ice decay (3.8 to 122 μmol O2 L−1).
We finally highlight the key issues to solve for more accurate NCP estimates in the future. 2014/09/24 - 13:58

The influence of ocean acidification on nitrogen regeneration and nitrous oxide production in the northwest European shelf seaBiogeosciences, 11, 4985-5005, 2014Author(s): D. R. Clark, I. J. Brown, A. P. Rees, P. J. Somerfield, and P. I. MillerThe assimilation and regeneration of dissolved inorganic nitrogen, and the
concentration of N2O, was investigated at stations located in the NW
European shelf sea during June/July 2011. These observational measurements
within the photic zone demonstrated the simultaneous regeneration and
assimilation of NH4+, NO2− and NO3−.
NH4+ was assimilated at 1.82–49.12 nmol N L−1 h−1 and regenerated at
3.46–14.60 nmol N L−1 h−1; NO2-
was assimilated at 0–2.08 nmol N L−1 h−1
and regenerated at 0.01–1.85 nmol N L−1 h−1; NO3− was assimilated at 0.67–18.75 nmol N L−1 h−1 and regenerated at
0.05–28.97 nmol N L−1 h−1. Observations implied that these processes were closely coupled at the
regional scale and that nitrogen recycling played an important role in sustaining
phytoplankton growth during the summer. The [N2O], measured in water
column profiles, was 10.13 ± 1.11 nmol L−1 and
did not strongly diverge from atmospheric equilibrium indicating that
sampled marine regions were neither a strong source nor sink of N2O to
the atmosphere. Multivariate analysis of data describing water column
biogeochemistry and its links to N-cycling activity failed to explain the
observed variance in rates of N-regeneration and N-assimilation,
possibly due to the limited number of process rate observations. In the
surface waters of five further stations, ocean acidification (OA) bioassay
experiments were conducted to investigate the response of NH4+
oxidising and regenerating organisms to simulated OA conditions, including
the implications for [N2O]. Multivariate analysis was undertaken which
considered the complete bioassay data set of measured variables describing
changes in N-regeneration rate, [N2O] and the biogeochemical
composition of seawater. While anticipating biogeochemical differences
between locations, we aimed to test the hypothesis that the underlying
mechanism through which pelagic N-regeneration responded to simulated OA
conditions was independent of location. Our objective was to develop a
mechanistic understanding of how NH4+ regeneration, NH4+
oxidation and N2O production responded to OA. Results indicated that
N-regeneration process responses to OA treatments were location specific;
no mechanistic understanding of how N-regeneration processes respond to
OA in the surface ocean of the NW European shelf sea could be developed. 2014/09/24 - 13:58

Organomineral nanocomposite carbon burial during Oceanic Anoxic Event 2Biogeosciences, 11, 4971-4983, 2014Author(s): S. C. Löhr and M. J. KennedyOrganic carbon (OC) enrichment in sediments deposited during Oceanic Anoxic
Events (OAEs) is commonly attributed to elevated productivity and marine
anoxia. We find that OC enrichment in the late Cenomanian aged OAE 2 at the
Demerara Rise was controlled by the co-occurrence of anoxic bottom water,
sufficient productivity to saturate available mineral surfaces, and variable
deposition of high surface area detrital smectite clay. Redox indicators show
consistently oxygen-depleted conditions, while a strong correlation between
OC concentration and sediment mineral surface area (R2 = 0.92) occurs
across a range of total organic carbon (TOC) values from 9 to 33%. X-ray
diffraction data indicate the intercalation of OC in smectite interlayers,
while electron, synchrotron infrared and X-ray microscopy show an intimate
association between clay minerals and OC, consistent with preservation of OC
as organomineral nanocomposites and aggregates rather than discrete,
μm-scale pelagic detritus. Since the consistent ratio between TOC
and mineral surface area suggests that excess OC relative to surface area is
lost, we propose that it is the varying supply of smectite that best explains
variable organic enrichment against a backdrop of continuous anoxia, which is
conducive to generally high TOC during OAE 2 at the Demerara Rise. Smectitic
clays are unique in their ability to form stable organomineral nanocomposites
and aggregates that preserve organic matter, and are common weathering
products of continental volcanic deposits. An increased flux of smectite
coinciding with high carbon burial is consistent with evidence for widespread
volcanism during OAE 2, so that organomineral carbon burial may represent a
potential feedback to volcanic degassing of CO2. 2014/09/24 - 13:58

Preface "Biogeochemistry and ecosystems in the western north Pacific continental margins under climate change and anthropogenic forcing"Biogeosciences, 11, 4967-4969, 2014Author(s): K.-K. Liu, M.-H. Dai, K.-R. Kim, and G.-C. Gong 2014/09/17 - 00:03

Reduction of ferrihydrite with adsorbed and coprecipitated organic matter: microbial reduction by Geobacter bremensis vs. abiotic reduction by Na-dithioniteBiogeosciences, 11, 4953-4966, 2014Author(s): K. Eusterhues, A. Hädrich, J. Neidhardt, K. Küsel, T. F. Keller, K. D. Jandt, and K. U. TotscheFerrihydrite is a widespread poorly crystalline Fe oxide which
becomes easily coated by natural organic matter in the environment. This
mineral-bound organic matter entirely changes the mineral surface properties
and therefore the reactivity of the original mineral. Here, we investigated
2-line ferrihydrite, ferrihydrite with adsorbed organic matter, and
ferrihydrite coprecipitated with organic matter for microbial and abiotic
reduction of Fe(III). Ferrihydrite-organic matter associations with
different organic matter loadings were reduced either by Geobacter bremensis or abiotically by
Na-dithionite. Both types of experiments showed decreasing initial Fe-reduction rates and decreasing degrees of reduction with increasing amounts
of mineral-bound organic matter. At similar organic matter loadings,
coprecipitated ferrihydrites were more reactive than ferrihydrites with
adsorbed organic matter. The difference can be explained by the smaller
crystal size and poor crystallinity of such coprecipitates. At small organic
matter loadings the poor crystallinity of coprecipitates led to even faster
Fe-reduction rates than found for pure ferrihydrite. The amount of
mineral-bound organic matter also affected the formation of secondary
minerals: goethite was only found after reduction of organic matter-free
ferrihydrite and siderite was only detected when ferrihydrites with
relatively low amounts of mineral-bound organic matter were reduced. We
conclude that direct contact of G. bremensis to the Fe oxide mineral surface was
inhibited by attached organic matter. Consequently, mineral-bound organic
matter shall be taken into account as a factor in slowing down reductive
dissolution. 2014/09/17 - 00:03

Responses of nitrous oxide emissions to nitrogen and phosphorus additions in two tropical plantations with N-fixing vs. non-N-fixing tree speciesBiogeosciences, 11, 4941-4951, 2014Author(s): W. Zhang, X. Zhu, Y. Luo, R. Rafique, H. Chen, J. Huang, and J. MoLeguminous tree plantations at phosphorus (P) limited sites may result in
excess nitrogen (N) and higher rates of nitrous oxide (N2O) emissions.
However, the effects of N and P applications on soil N2O emissions from
plantations with N-fixing vs. non-N-fixing tree species have rarely been
studied in the field. We conducted an experimental manipulation of N and/or
P additions in two plantations with Acacia auriculiformis (AA, N-fixing)
and Eucalyptus urophylla (EU, non-N-fixing) in South China. The objective was to determine the effects of N or
P addition alone, as well as NP application together on soil N2O
emissions from these tropical plantations. We found that the average
N2O emission from control was greater in the AA (2.3 ± 0.1 kg
N2O–N ha−1 yr−1) than in EU plantation (1.9 ± 0.1 kg
N2O–N ha−1 yr−1). For the AA plantation, N addition stimulated
N2O emission from the soil while P addition did not. Applications of N
with P together significantly decreased N2O emission compared to
N addition alone, especially in the high-level treatments (decreased by
18%). In the EU plantation, N2O emissions significantly decreased in
P-addition plots compared with the controls; however, N and NP additions
did not. The different response of N2O emission to N or P addition was
attributed to the higher initial soil N status in the AA than that of EU
plantation, due to symbiotic N fixation in the former. Our result suggests
that atmospheric N deposition potentially stimulates N2O emissions from
leguminous tree plantations in the tropics, whereas P fertilization has the
potential to mitigate N-deposition-induced N2O emissions from such
plantations. 2014/09/17 - 00:03

Consistent increase in dimethyl sulfide (DMS) in response to high CO2 in five shipboard bioassays from contrasting NW European watersBiogeosciences, 11, 4925-4940, 2014Author(s): F. E. Hopkins and S. D. ArcherThe ubiquitous marine trace gas dimethyl sulfide (DMS) comprises the
greatest natural source of sulfur to the atmosphere and is a key player in
atmospheric chemistry and climate. We explore the short-term response of
DMS production and cycling and that of its algal precursor dimethyl sulfoniopropionate (DMSP) to elevated carbon dioxide (CO2) and ocean acidification (OA)
in five 96 h shipboard bioassay experiments. Experiments were performed in
June and July 2011, using water collected from contrasting sites in NW European
waters (Outer Hebrides, Irish Sea, Bay of Biscay, North Sea). Concentrations
of DMS and DMSP, alongside rates of DMSP synthesis and DMS production and
consumption, were determined during all experiments for ambient CO2 and
three high-CO2 treatments (550, 750, 1000 μatm). In general, the
response to OA throughout this region showed little variation, despite
encompassing a range of biological and biogeochemical conditions. We
observed consistent and marked increases in DMS concentrations relative to
ambient controls (110% (28–223%) at 550 μatm, 153% (56–295%) at 750 μatm and 225% (79–413%) at 1000 μatm),
and decreases in DMSP concentrations (28% (18–40%)
at 550 μatm, 44% (18–64%) at 750 μatm and 52%
(24–72%) at 1000 μatm). Significant decreases in DMSP
synthesis rate constants (μDMSP, d−1) and DMSP production rates
(nmol d−1) were observed in two experiments (7–90% decrease),
whilst the response under high CO2 from the remaining experiments was
generally indistinguishable from ambient controls. Rates of bacterial DMS
gross consumption and production gave weak and inconsistent responses to
high CO2. The variables and rates we report increase our
of the processes behind the response to OA. This could provide the
opportunity to improve upon mesocosm-derived empirical modelling
relationships and to move towards a mechanistic approach for predicting future
DMS concentrations. 2014/09/17 - 00:03

Nitrate source identification in the Baltic Sea using its isotopic ratios in combination with a Bayesian isotope mixing modelBiogeosciences, 11, 4913-4924, 2014Author(s): F. Korth, B. Deutsch, C. Frey, C. Moros, and M. VossNitrate (NO3−) is the major nutrient responsible for coastal
eutrophication worldwide and its production is related to intensive food
production and fossil-fuel combustion. In the Baltic Sea NO3− inputs
have increased 4-fold over recent decades and now remain constantly
high. NO3− source identification is therefore an important
consideration in environmental management strategies. In this study focusing
on the Baltic Sea, we used a method to estimate the proportional
contributions of NO3− from atmospheric deposition, N2 fixation,
and runoff from pristine soils as well as from agricultural land. Our
approach combines data on the dual isotopes of NO3−
(δ15N-NO3− and δ18O-NO3−) in winter
surface waters with a Bayesian isotope mixing model (Stable Isotope Analysis
in R, SIAR). Based on data gathered from 47 sampling locations over the
entire Baltic Sea, the majority of the NO3− in the southern Baltic
was shown to derive from runoff from agricultural land (33–100%),
whereas in the northern Baltic, i.e. the Gulf of Bothnia, NO3−
originates from nitrification in pristine soils (34–100%). Atmospheric
deposition accounts for only a small percentage of NO3− levels in the
Baltic Sea, except for contributions from northern rivers, where the levels
of atmospheric NO3− are higher. An additional important source in the
central Baltic Sea is N2 fixation by diazotrophs, which contributes
49–65% of the overall NO3− pool at this site. The results
obtained with this method are in good agreement with source estimates based
upon δ15N values in sediments and a three-dimensional ecosystem
model, ERGOM. We suggest that this approach can be easily modified to
determine NO3− sources in other marginal seas or larger near-coastal
areas where NO3− is abundant in winter surface waters when
fractionation processes are minor. 2014/09/17 - 00:03

Assessing the spatial variability in peak season CO2 exchange characteristics across the Arctic tundra using a light response curve parameterizationBiogeosciences, 11, 4897-4912, 2014Author(s): H. N. Mbufong, M. Lund, M. Aurela, T. R. Christensen, W. Eugster, T. Friborg, B. U. Hansen, E. R. Humphreys, M. Jackowicz-Korczynski, L. Kutzbach, P. M. Lafleur, W. C. Oechel, F. J. W. Parmentier, D. P. Rasse, A. V. Rocha, T. Sachs, M. K. van der Molen, and M. P. TamstorfThis paper aims to assess the spatial variability in the response of
CO2 exchange to irradiance across the Arctic tundra during peak season
using light response curve (LRC) parameters. This investigation allows us to
better understand the future response of Arctic tundra under climatic
change. Peak season data were collected during different years (between 1998
and 2010) using the micrometeorological eddy covariance technique from 12
circumpolar Arctic tundra sites, in the range of 64–74° N.

The LRCs were generated for 14 days with peak net ecosystem exchange (NEE)
using an NEE–irradiance model. Parameters from LRCs represent site-specific
traits and characteristics describing the following: (a) NEE at light saturation
(Fcsat), (b) dark respiration (Rd), (c) light use efficiency
(α), (d) NEE when light is at 1000 μmol m−2 s−1
(Fc1000), (e) potential photosynthesis at light saturation
(Psat) and (f) the light compensation point (LCP).

Parameterization of LRCs was successful in predicting CO2 flux dynamics
across the Arctic tundra. We did not find any trends in LRC parameters
across the whole Arctic tundra but there were indications for temperature
and latitudinal differences within sub-regions like Russia and Greenland.
Together, leaf area index (LAI) and July temperature had a high explanatory power of the
variance in assimilation parameters (Fcsat, Fc1000 and Psat,
thus illustrating the potential for upscaling CO2 exchange for the
whole Arctic tundra. Dark respiration was more variable and less correlated
to environmental drivers than were assimilation parameters. This indicates
the inherent need to include other parameters such as nutrient availability,
substrate quantity and quality in flux monitoring activities. 2014/09/17 - 00:03

Flexible C : N ratio enhances metabolism of large phytoplankton when resource supply is intermittentBiogeosciences, 11, 4881-4895, 2014Author(s): D. Talmy, J. Blackford, N. J. Hardman-Mountford, L. Polimene, M. J. Follows, and R. J. GeiderPhytoplankton cell size influences particle sinking rate, food web
interactions and biogeographical distributions. We present a model
in which the uptake, storage and assimilation of nitrogen and carbon
are explicitly resolved in different-sized phytoplankton cells. In
the model, metabolism and cellular C : N ratio are influenced by
the accumulation of carbon polymers such as carbohydrate and lipid,
which is greatest when cells are nutrient starved, or exposed to
high light. Allometric relations and empirical data sets are used to
constrain the range of possible C : N, and indicate that larger cells
can accumulate significantly more carbon storage compounds than
smaller cells. When forced with extended periods of darkness
combined with brief exposure to saturating irradiance, the model
predicts organisms large enough to accumulate significant carbon
reserves may on average synthesize protein and other functional
apparatus up to five times faster than smaller organisms. The
advantage of storage in terms of average daily protein synthesis
rate is greatest when modeled organisms were previously nutrient
starved, and carbon storage reservoirs saturated. Small organisms
may therefore be at a disadvantage in terms of average daily growth
rate in environments that involve prolonged periods of darkness and
intermittent nutrient limitation. We suggest this mechanism is
a significant constraint on phytoplankton C : N variability and
cell size distribution in different oceanic regimes. 2014/09/13 - 13:43

Optimizing sample pretreatment for compound-specific stable carbon isotopic analysis of amino sugars in marine sedimentBiogeosciences, 11, 4869-4880, 2014Author(s): R. Zhu, Y.-S. Lin, J. S. Lipp, T. B. Meador, and K.-U. HinrichsAmino sugars are quantitatively
significant constituents of soil and marine sediment, but their sources and
turnover in environmental samples remain poorly understood. The stable carbon
isotopic composition of amino sugars can provide information on the
lifestyles of their source organisms and can be monitored during incubations
with labeled substrates to estimate the turnover rates of microbial
populations. However, until now, such investigation has been carried out only
with soil samples, partly because of the much lower abundance of amino sugars
in marine environments. We therefore optimized a procedure for
compound-specific isotopic analysis of amino sugars in marine sediment,
employing gas chromatography–isotope ratio mass spectrometry. The whole
procedure consisted of hydrolysis, neutralization, enrichment, and
derivatization of amino sugars. Except for the derivatization step, the
protocol introduced negligible isotopic fractionation, and the minimum
requirement of amino sugar for isotopic analysis was 20 ng, i.e., equivalent
to ~8 ng of amino sugar carbon. Compound-specific stable carbon
isotopic analysis of amino sugars obtained from marine sediment extracts
indicated that glucosamine and galactosamine were mainly derived from organic
detritus, whereas muramic acid showed isotopic imprints from indigenous
bacterial activities. The δ13C analysis of amino sugars provides a
valuable addition to the biomarker-based characterization of microbial
metabolism in the deep marine biosphere, which so far has been lipid oriented
and biased towards the detection of archaeal signals. 2014/09/13 - 13:43

Impact of river discharge, upwelling and vertical mixing on the nutrient loading and productivity of the Canadian Beaufort ShelfBiogeosciences, 11, 4853-4868, 2014Author(s): J.-É. Tremblay, P. Raimbault, N. Garcia, B. Lansard, M. Babin, and J. GagnonThe concentrations and elemental stoichiometry of particulate and dissolved
pools of carbon (C), nitrogen (N), phosphorus (P) and silicon (Si) on the
Canadian Beaufort Shelf during summer 2009 (MALINA program) were assessed
and compared with those of surface waters provided by the Mackenzie river as
well as by winter mixing and upwelling of upper halocline waters at the
shelf break. Neritic surface waters showed a clear enrichment in dissolved
and particulate organic carbon (DOC and POC, respectively), nitrate, total
particulate nitrogen (TPN) and dissolved organic nitrogen (DON) originating
from the river. Silicate as well as bulk DON and DOC declined in a
near-conservative manner away from the delta's outlet, whereas nitrate
dropped non-conservatively to very low background concentrations inside the
brackish zone. By contrast, the excess of soluble reactive P (SRP) present
in oceanic waters declined in a non-conservative manner toward the river
outlet, where concentrations were very low and consistent with P shortage in
the Mackenzie River. These opposite gradients imply that the admixture of
Pacific-derived, SRP-rich water is necessary to allow phytoplankton to use
river-derived nitrate and to a lesser extent DON. A coarse budget based on
concurrent estimates of primary production shows that river N deliveries
support a modest fraction of primary production when considering the entire
shelf, due to the ability of phytoplankton to thrive in the subsurface
chlorophyll maximum beneath the thin, nitrate-depleted river plume. Away
from shallow coastal bays, local elevations in the concentration of primary
production and dissolved organic constituents were consistent with upwelling
at the shelf break. By contrast with shallow winter mixing, nutrient
deliveries by North American rivers and upwelling relax surface communities
from N limitation and permit a more extant utilization of the excess SRP
entering through the Bering Strait. In this context, increased nitrogen supply
by rivers and upwelling potentially alters the vertical distribution of the
excess P exported into the North Atlantic. 2014/09/13 - 13:43

The 129-iodine content of subtropical Pacific waters: impact of Fukushima and other anthropogenic 129-iodine sourcesBiogeosciences, 11, 4839-4852, 2014Author(s): T. P. Guilderson, S. J. Tumey, T. A. Brown, and K. O. BuesselerResults obtained from a dedicated radiochemistry cruise approximately 100 days after
the 11 March 2011 Tohoku earthquake and subsequent disaster at
the Fukushima Daiichi Nuclear Power Plant show that Fukushima derived
radionuclides in the nearby ocean environment had penetrated, on average, to
≤250 m depth (1026.5 kg m3 potential density surface). The excess
inventory of Fukushima-derived 129I in the region (∼150 000 km2) sampled during the cruise is estimated to have been
between 0.89 and 1.173 billion Bq (∼136 to ∼179 grams) of 129I. Based on a tight tracer–tracer relation with
134Cs (or 137Cs) and estimates that most of the excess cesium is
due to direct discharge, we infer that much of the excess 129I is from
direct (non-atmospheric deposition) discharge. After taking into account
oceanic transport, we estimate the direct discharge, i.e., that directly
released into the ocean, off Fukushima to have been ∼1 kg 129I. Although this small pulse is dwarfed by the ~90 kg
of weapons-testing-derived 129I that was released into the environment
in the late 1950s and early 1960s, it should be possible to use Fukushima-derived 129I and other radionuclides (e.g., 134, 137Cs) to study
transport and entrainment processes along and across the Kuroshio Current. 2014/09/13 - 13:43

A red tide alga grown under ocean acidification upregulates its tolerance to lower pH by increasing its photophysiological functionsBiogeosciences, 11, 4829-4837, 2014Author(s): S. Chen, J. Beardall, and K. GaoPhaeocystis globosa, a red tide alga, often forms blooms in or adjacent to coastal waters and
experiences changes in pH and seawater carbonate chemistry caused by either
diel/periodic fluctuation in biological activity, human activity or, in the
longer term, ocean acidification due to atmospheric CO2 rise. We
examined the photosynthetic physiology of this species while growing it
under different pH levels induced by CO2 enrichment and investigated
its acclimation to carbonate chemistry changes under different light levels.
Short-term exposure to reduced pHnbs (7.70) decreased the alga's
photosynthesis and light use efficiency. However, acclimation to the reduced
pH level for 1–19 generations led to recovered photosynthetic activity,
being equivalent to that of cells grown under pH 8.07 (control), though such
acclimation required a different time span (number of generations) under
different light regimes. The low-pH-grown cells increased their contents of
chlorophyll and carotenoids with prolonged acclimation to the acidification,
with increased photosynthetic quantum yield and decreased non-photochemical
quenching. The specific growth rate of the low-pH-grown cells also increased
to emulate that grown under the ambient pH level. This study clearly shows
that \textit{Phaeocystis globosa} is able to acclimate to seawater acidification by increasing its
energy capture and decreasing its non-photochemical energy loss. 2014/09/13 - 13:43

Comparing the influence of net and gross anthropogenic land-use and land-cover changes on the carbon cycle in the MPI-ESMBiogeosciences, 11, 4817-4828, 2014Author(s): S. Wilkenskjeld, S. Kloster, J. Pongratz, T. Raddatz, and C. H. ReickGlobal vegetation models traditionally treat anthropogenic land-use and land-cover changes (LULCCs)
only as the changes in vegetation cover seen from one year to the next (net transitions). This
approach ignores subgrid-scale processes such as shifting cultivation which do not affect the net
vegetation distribution but which have an impact on the carbon budget. The differences in the
carbon stocks feed back on processes like wildfires and desert formation. The simulations for the
Coupled Model Intercomparison Project Phase 5 (CMIP5) all describe LULCCs using the "Land-Use
Harmonization Dataset". Though this dataset describes such subgrid-scale processes (gross
transitions), some of the CMIP5 models still use the traditional approach. Using JSBACH/CBALANCE
– the land carbon component of the Max Planck Institute Earth System Model (MPI-ESM), this study
demonstrates how this potentially leads to a severe underestimation of the carbon emissions from LULCCs
Using net transitions lowers the average land-use emissions from 1.44 to
0.90 Pg C yr−1
(38%) during the historical period (1850–2005) – a total lowering by 85 Pg C. The
difference between the methods is smaller in the RCP scenarios (2006–2100) but in RCP2.6 and RCP8.5
still cumulates to 30–40 Pg C (on average 0.3–0.4 Pg C yr−1 or 13–25%).
In RCP4.5 essentially no difference between the methods is found. Results from models using net
transitions are furthermore found to be sensitive to model resolution. 2014/09/13 - 13:43

Response of CH4 emissions to moss removal and N addition in boreal peatland of northeast ChinaBiogeosciences, 11, 4809-4816, 2014Author(s): H. N. Meng, C. C. Song, Y. Q. Miao, R. Mao, and X. W. WangBoreal peatlands are an important natural source of atmospheric methane
(CH4). Recently, boreal peatlands have been experiencing increased
nitrogen (N) availability and decreased moss production. However, little is
known about the interactive effect of moss and N availability on CH4
emissions in boreal peatlands. In this study, the effects of moss removal and
N addition (6 g N m−2 yr−1) on CH4 emissions were
examined during the growing seasons of 2011, 2012 and 2013 in a boreal
peatland in the Great Hinggan Mountain of northeast China. Notably, the
response of CH4 emissions to moss removal and N addition varied with
experimental duration. Moss removal and N addition did not affect CH4
emissions in 2011 and 2012, but respectively reduced CH4 emissions by
50% and 66% in 2013. However, moss removal and N addition did not
produce an interactive effect on CH4 emissions. Consequently, moss
removal plus N addition had no effect on CH4 emissions in 2011 and
2012, but decreased CH4 emissions by 68% in 2013. These results
suggest that the effects of moss removal and N enrichment on CH4
emissions are time-dependent in boreal peatlands, and also imply that
increased N availability and decreased moss growth would independently
inhibit CH4 emissions in the boreal peatlands of northeast China. 2014/09/13 - 13:43

Temperature sensitivity of organic-matter decay in tidal marshesBiogeosciences, 11, 4801-4808, 2014Author(s): M. L. Kirwan, G. R. Guntenspergen, and J. A. LangleyApproximately half of marine carbon sequestration takes place in coastal
wetlands, including tidal marshes, where organic matter contributes to soil
elevation and ecosystem persistence in the face of sea-level rise. The
long-term viability of marshes and their carbon pools depends, in part, on
how the balance between productivity and decay responds to climate change.
Here, we report the sensitivity of labile soil organic-matter decay in tidal
marshes to seasonal and latitudinal variations in temperature measured over a
3-year period. We find a moderate increase in decay rate at warmer
temperatures (3–6% per °C, Q10 = 1.3–1.5). Despite the
profound differences between microbial metabolism in wetlands and uplands,
our results indicate a strong conservation of temperature sensitivity.
Moreover, simple comparisons with organic-matter production suggest that
elevated atmospheric CO2 and warmer temperatures will accelerate carbon
accumulation in marsh soils, and potentially enhance their ability to survive
sea-level rise. 2014/09/13 - 13:43

Contrasted Saharan dust events in LNLC environments: impact on nutrient dynamics and primary productionBiogeosciences, 11, 4783-4800, 2014Author(s): C. Ridame, J. Dekaezemacker, C. Guieu, S. Bonnet, S. L'Helguen, and F. MalienThe response of the phytoplanktonic community (primary production and algal
biomass) to contrasted Saharan dust events (wet and dry deposition) was
studied in the framework of the DUNE ("a DUst experiment in a low-Nutrient,
low-chlorophyll Ecosystem") project. We simulated realistic dust deposition
events (10 g m−2) into large mesocosms (52 m3). Three distinct
dust addition experiments were conducted in June 2008 (DUNE-1-P: simulation
of a wet deposition; DUNE-1-Q: simulation of a dry deposition) and 2010
(DUNE-2-R1 and DUNE-2-R2: simulation of two successive wet depositions) in
the northwestern oligotrophic Mediterranean Sea. No changes in primary
production (PP) and chlorophyll a concentrations (Chl a) were observed
after a dry deposition event, while a wet deposition event resulted in a
rapid (24 h after dust addition), strong (up to 2.4-fold) and long (at least
a week in duration) increase in PP and Chl a. We show that, in addition to
being a source of dissolved inorganic phosphorus (DIP), simulated wet
deposition events were also a significant source of nitrate (NO3−)
(net increases up to +9.8 μM NO3− at 0.1 m in depth) to
the nutrient-depleted surface waters, due to cloud processes and mixing with
anthropogenic species such as HNO3. The dry deposition event was shown
to be a negligible source of NO3−. By transiently increasing DIP and
NO3- concentrations in N–P starved surface waters, wet deposition of
Saharan dust was able to relieve the potential N or NP co-limitation of the
phytoplanktonic activity. Due to the higher input of NO3− relative to
DIP, and taking into account the stimulation of the biological activity, a
wet deposition event resulted in a strong increase in the
NO3−/DIP ratio, from initially less than 6, to over 150
at the end of the DUNE-2-R1 experiment, suggesting a switch from an initial N
or NP co-limitation towards a severe P limitation. We also show that the
contribution of new production to PP strongly increased after wet dust
deposition events, from initially 15% to 60–70% 24 h after
seeding, indicating a switch from a regenerated-production based system to a
new-production based system. DUNE experiments show that wet and dry dust
deposition events induce contrasting responses of the phytoplanktonic
community due to differences in the atmospheric supply of bioavailable new
nutrients. Our results from original mesocosm experiments demonstrate that
atmospheric dust wet deposition greatly influences primary productivity and
algal biomass in LNLC environments through changes in the nutrient stocks,
and alters the NO3−/DIP ratio, leading to a switch in the
nutrient limitation of the phytoplanktonic activity. 2014/09/13 - 13:43

Morphology of Emiliania huxleyi coccoliths on the northwestern European shelf – is there an influence of carbonate chemistry?Biogeosciences, 11, 4771-4782, 2014Author(s): J. R. Young, A. J. Poulton, and T. TyrrellWithin the context of the UK Ocean Acidification project, Emiliania huxleyi (type A)
coccolith morphology was examined from samples collected during cruise D366.
In particular, a morphometric study of coccolith size and degree of
calcification was made on scanning electron microscope images of samples
from shipboard CO2 perturbation experiments and from a set of
environmental samples with significant variation in calcite saturation state
(Ωcalcite). One bioassay in particular (E4 from the southern
North Sea) yielded unambiguous results – in this bioassay exponential growth
from a low initial cell density occurred with no nutrient enrichment and
coccosphere numbers increased tenfold during the experiment. The samples
with elevated CO2 saw significantly reduced coccolithophore growth.
However, coccolithophore morphology was not significantly affected by the
changing CO2 conditions even under the highest levels of perturbation
(1000 μatm CO2). Environmental samples similarly showed no
correlation of coccolithophore morphology with calcite saturation state.
Some variation in coccolith size and degree of calcification does occur but
this seems to be predominantly due to genotypic differentiation between
populations on the shelf and in the open ocean. 2014/09/13 - 13:43