Role of zooplankton dynamics for Southern Ocean phytoplankton   biomass and global biogeochemical cycles

Abstract. Global ocean biogeochemistry models currently employed in climate change projections use highly simplified representations of pelagic food webs. These food webs do not necessarily include critical pathways by which ecosystems interact with ocean biogeochemistry and climate. Here we present a global biogeochemical model which incorporates ecosystem dynamics based on the representation of ten plankton functional types (PFTs); six types of phytoplankton, three types of zooplankton, and heterotrophic bacteria. We improved the representation of zooplankton dynamics in our model through (a) the explicit inclusion of large, slow-growing zooplankton, and (b) the introduction of trophic cascades among the three zooplankton types. We use the model to quantitatively assess the relative roles of iron vs. grazing in determining phytoplankton biomass in the Southern Ocean High Nutrient Low Chlorophyll (HNLC) region during summer. When model simulations do not represent crustacean macrozooplankton grazing, they systematically overestimate Southern Ocean chlorophyll biomass during the summer, even when there was no iron deposition from dust. When model simulations included the developments of the zooplankton component, the simulation of phytoplankton biomass improved and the high chlorophyll summer bias in the Southern Ocean HNLC region largely disappeared. Our model results suggest that the observed low phytoplankton biomass in the Southern Ocean during summer is primarily explained by the dynamics of the Southern Ocean zooplankton community rather than iron limitation. This result has implications for the representation of global biogeochemical cycles in models as zooplankton faecal pellets sink rapidly and partly control the carbon export to the intermediate and deep ocean.

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Role of zooplankton dynamics for Southern Ocean phytoplankton biomass and global biogeochemical cycles

Biogeosciences ◽

10.5194/bg-13-4111-2016 ◽

2016 ◽

Vol 13 (14) ◽

pp. 4111-4133 ◽

Cited By ~ 34

Author(s):

Corinne Le Quéré ◽

Erik T. Buitenhuis ◽

Róisín Moriarty ◽

Séverine Alvain ◽

Olivier Aumont ◽

...

Keyword(s):

Southern Ocean ◽

Food Webs ◽

Phytoplankton Biomass ◽

Trophic Cascades ◽

Biogeochemical Cycles ◽

Model Simulations ◽

Zooplankton Dynamics ◽

Ocean Biogeochemistry ◽

Global Biogeochemical Cycles ◽

Slow Growing

Abstract. Global ocean biogeochemistry models currently employed in climate change projections use highly simplified representations of pelagic food webs. These food webs do not necessarily include critical pathways by which ecosystems interact with ocean biogeochemistry and climate. Here we present a global biogeochemical model which incorporates ecosystem dynamics based on the representation of ten plankton functional types (PFTs): six types of phytoplankton, three types of zooplankton, and heterotrophic procaryotes. We improved the representation of zooplankton dynamics in our model through (a) the explicit inclusion of large, slow-growing macrozooplankton (e.g. krill), and (b) the introduction of trophic cascades among the three zooplankton types. We use the model to quantitatively assess the relative roles of iron vs. grazing in determining phytoplankton biomass in the Southern Ocean high-nutrient low-chlorophyll (HNLC) region during summer. When model simulations do not include macrozooplankton grazing explicitly, they systematically overestimate Southern Ocean chlorophyll biomass during the summer, even when there is no iron deposition from dust. When model simulations include a slow-growing macrozooplankton and trophic cascades among three zooplankton types, the high-chlorophyll summer bias in the Southern Ocean HNLC region largely disappears. Our model results suggest that the observed low phytoplankton biomass in the Southern Ocean during summer is primarily explained by the dynamics of the Southern Ocean zooplankton community, despite iron limitation of phytoplankton community growth rates. This result has implications for the representation of global biogeochemical cycles in models as zooplankton faecal pellets sink rapidly and partly control the carbon export to the intermediate and deep ocean.

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Detecting Climate Fingerprints in Southern Ocean Carbon using a Biogeochemical Ocean Model

10.5194/egusphere-egu21-11116 ◽

2021 ◽

Author(s):

Rebecca Wright ◽

Corinne Le Quéré ◽

Erik Buitenhuis ◽

Dorothee Bakker

Keyword(s):

Climate Change ◽

Climate Variability ◽

Southern Ocean ◽

Observational Data ◽

Ecosystem Dynamics ◽

Global Ocean ◽

Subsurface Waters ◽

Climatic Drivers ◽

Ocean Carbon ◽

And Storage

The Southern Ocean plays an important role in the uptake, transport and storage of carbon by the global oceans. These properties are dominated by the response to the rise in anthropogenic CO2 in the atmosphere, but they are modulated by climate variability and climate change. Here we explore the effect of climate variability and climate change on ocean carbon uptake and storage in the Southern Ocean. We assess the extent to which climate change may be distinguishable from the anthropogenic CO2 signal and from the natural background variability. We use a combination of biogeochemical ocean modelling and observations from the GLODAPv2020 database to detect climate fingerprints in dissolved inorganic carbon (DIC).We conduct an ensemble of hindcast model simulations of the period 1920-2019, using a global ocean biogeochemical model which incorporates plankton ecosystem dynamics based on twelve plankton functional types. We use the model ensemble to isolate the changes in DIC due to rising anthropogenic CO2 alone and the changes due to climatic drivers (both climate variability and climate change), to determine their relative roles in the emerging total DIC trends and patterns. We analyse these DIC trends for a climate fingerprint over the past four decades, across spatial scales from the Southern Ocean, to basin level and down to regional ship transects. Highly sampled ship transects were extracted from GLODAPv2020 to obtain locations with the maximum spatiotemporal coverage, to reduce the inherent biases in patchy observational data. Model results were sampled to the ship transects to compare the climate fingerprints directly to the observational data.Model results show a substantial change in DIC over a 35-year period, with a range of more than +/- 30 &#181;mol/L. In the surface ocean, both anthropogenic CO2 and climatic drivers act to increase DIC concentration, with the influence of anthropogenic CO2 dominating at lower latitudes and the influence of climatic drivers dominating at higher latitudes. In the deep ocean, the anthropogenic CO2 generally acts to increase DIC except in the subsurface waters at lower latitudes, while climatic drivers act to decrease DIC concentration. The combined fingerprint of anthropogenic CO2 and climatic drivers on DIC concentration is for an increasing trend at the surface and decreasing trends in low latitude subsurface waters. Preliminary comparison of the model fingerprints to observational ship transects will also be presented.

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The Role of Restricted Basins in Global Biogeochemical Cycles

10.5194/egusphere-egu2020-7533 ◽

2020 ◽

Author(s):

Alexandra Turchyn

Keyword(s):

Isotopic Composition ◽

Chemical Weathering ◽

Biogeochemical Cycles ◽

Biogeochemical Cycle ◽

Global Ocean ◽

Sulfur Isotopic Composition ◽

Sediment Biogeochemistry ◽

Shelf Slope ◽

Salt Deposits ◽

Global Biogeochemical Cycles

The formation of restricted basins isolates seawater from the global ocean and allows the formation of salt deposits, often because restricted basins can have minor connectivity to the global ocean and thus can fill and evaporate many times over. The formation of salts removes ions from the global ocean, potentially decreasing their concentration elsewhere and leading to an alteration of their biogeochemical cycle.&#160; The subsequent exposure and chemical weathering of these salt deposits changes the source of these elements back into the global ocean and can influence their biogeochemical cycles for a long time after the formation of the restricted basin.&#160; &#160;Sediment biogeochemistry in restricted basins also differs from most global continental shelf, slope, and deep-sea sediments. The formation of sedimentary minerals and their subsequent diagenesis means that the amount and isotopic composition of deposited minerals in restricted basins can differ greatly from those in the global ocean. In this talk I am going to explore how the formation of restricted basins, including epicontinental seas and isolated seas, has influenced the biogeochemical cycle of carbon and sulfur over the course of the last 65 million years.&#160; I am going to use a combination of new measurements on the carbon and sulfur isotopic composition of the ocean over this time to explore how different types of restricted basins influence global biogeochemical cycles in the rest of the ocean. I will argue that the formation of restricted basins has been important in driving changes in the carbon and sulfur isotopic composition of the ocean over time, linking changes in ocean chemistry to tectonics.

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Environmental forcing and Southern Ocean marine predator populations: effects of climate change and variability

Philosophical Transactions of the Royal Society B Biological Sciences ◽

10.1098/rstb.2006.1953 ◽

2007 ◽

Vol 362 (1488) ◽

pp. 2351-2365 ◽

Cited By ~ 122

Author(s):

P.N Trathan ◽

J Forcada ◽

E.J Murphy

Keyword(s):

Climate Change ◽

Southern Ocean ◽

Food Webs ◽

Time Scales ◽

Trophic Level ◽

Global Ocean ◽

Ecosystem Structure ◽

Marine Predator ◽

Enso Events ◽

Biological Responses

The Southern Ocean is a major component within the global ocean and climate system and potentially the location where the most rapid climate change is most likely to happen, particularly in the high-latitude polar regions. In these regions, even small temperature changes can potentially lead to major environmental perturbations. Climate change is likely to be regional and may be expressed in various ways, including alterations to climate and weather patterns across a variety of time-scales that include changes to the long interdecadal background signals such as the development of the El Niño–Southern Oscillation (ENSO). Oscillating climate signals such as ENSO potentially provide a unique opportunity to explore how biological communities respond to change. This approach is based on the premise that biological responses to shorter-term sub-decadal climate variability signals are potentially the best predictor of biological responses over longer time-scales. Around the Southern Ocean, marine predator populations show periodicity in breeding performance and productivity, with relationships with the environment driven by physical forcing from the ENSO region in the Pacific. Wherever examined, these relationships are congruent with mid-trophic-level processes that are also correlated with environmental variability. The short-term changes to ecosystem structure and function observed during ENSO events herald potential long-term changes that may ensue following regional climate change. For example, in the South Atlantic, failure of Antarctic krill recruitment will inevitably foreshadow recruitment failures in a range of higher trophic-level marine predators. Where predator species are not able to accommodate by switching to other prey species, population-level changes will follow. The Southern Ocean, though oceanographically interconnected, is not a single ecosystem and different areas are dominated by different food webs. Where species occupy different positions in different regional food webs, there is the potential to make predictions about future change scenarios.

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Relationship between Ocean Carbon and Heat Multidecadal Variability

Journal of Climate ◽

10.1175/jcli-d-17-0134.1 ◽

2018 ◽

Vol 31 (4) ◽

pp. 1467-1482 ◽

Cited By ~ 5

Author(s):

Jordan Thomas ◽

Darryn Waugh ◽

Anand Gnanadesikan

Keyword(s):

Southern Ocean ◽

Carbon Content ◽

Climate Model ◽

Deep Convection ◽

Heat Content ◽

Weddell Sea ◽

Global Ocean ◽

Multidecadal Variability ◽

Model Simulations ◽

Ocean Carbon

The global ocean serves as a critical sink for anthropogenic carbon and heat. While significant effort has been dedicated to quantifying the oceanic uptake of these quantities, less research has been conducted on the mechanisms underlying decadal-to-centennial variability in oceanic heat and carbon. Therefore, little is understood about how much such variability may have obscured or reinforced anthropogenic change. Here the relationship between oceanic heat and carbon content is examined in a suite of coupled climate model simulations that use different parameterization settings for mesoscale mixing. The differences in mesoscale mixing result in very different multidecadal variability, especially in the Weddell Sea where the characteristics of deep convection are drastically changed. Although the magnitude and frequency of variability in global heat and carbon content is different across the model simulations, there is a robust anticorrelation between global heat and carbon content in all simulations. Global carbon content variability is primarily driven by Southern Ocean carbon variability. This contrasts with global heat content variability. Global heat content is primarily driven by variability in the southern midlatitudes and tropics, which opposes the Southern Ocean variability.

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Nanoparticulate bioavailable iron minerals in icebergs and glaciers

Mineralogical Magazine ◽

10.1180/minmag.2008.072.1.345 ◽

2008 ◽

Vol 72 (1) ◽

pp. 345-348 ◽

Cited By ~ 28

Author(s):

R. Raiswell ◽

L. G. Benning ◽

L. Davidson ◽

M. Tranter

Keyword(s):

Southern Ocean ◽

Biogeochemical Cycles ◽

Low Ph ◽

Sulphide Oxidation ◽

Aeolian Dust ◽

Iron Minerals ◽

Global Biogeochemical Cycles ◽

Biogeochemical Hotspots

AbstractIce-hosted sediments in glaciers and icebergs from Antarctica and Svalbard contain authigenic nanoparticulates of schwertmannite, ferrihydrite and goethite that formed during sulphide oxidation. These phases indicate the existence of subglacial biogeochemical hotspots containing fluids of low pH (2—4), rich in dissolved Fe(III) and sulphate. Nanophase Fe is partially bioavailable and potentially important to global biogeochemical cycles, since the flux delivered by icebergs to the Southern Ocean is comparable to the flux of soluble, bioavailable Fe from aeolian dust.

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Modeling the physical drivers of the decadal variability of the Southern Ocean carbon uptake

10.5194/egusphere-egu21-8654 ◽

2021 ◽

Author(s):

Lavinia Patara ◽

Torge Martin ◽

Ivy Frenger ◽

Jan Klaus Rieck ◽

Chia-Te Chien

Keyword(s):

Southern Ocean ◽

Decadal Variability ◽

Open Ocean ◽

Global Ocean ◽

Carbon Uptake ◽

Positive Trend ◽

The Past ◽

Rate Of Increase ◽

Ocean Biogeochemistry ◽

Ocean Carbon

Observational estimates point to pronounced changes of the Southern Ocean carbon uptake in the past decades, but the mechanisms are still not fully understood. In this study we assess physical drivers of the Southern Ocean carbon uptake variability in a suite of global ocean biogeochemistry models with 0.5&#186;, 0.25&#186; and 0.1&#186; horizontal resolution as well as in a 3-member ensemble performed with an Earth System Model (ESM) sharing the same ocean biogeochemistry model. The ocean models show a positive trend of the Southern Ocean CO2 uptake in the past decades, with a weakening of its rate of increase in the 1990s. The 0.1&#186; model exhibits the strongest trend in the Southern Ocean carbon uptake.&#160;Different physical drivers of the carbon uptake variability and of its trends (such as changes in stratification, ventilation, overturning circulation, and SST) are analyzed. A particular focus of this study is to assess the role of open-ocean polynyas in driving Southern Ocean carbon uptake. Open-ocean polynyas in the Southern Ocean have pronounced climate fingerprints, such as reduced sea-ice coverage, heat loss by the ocean and enhanced bottom water formation, but their role for the Southern Ocean carbon uptake has been as yet little studied. To this end we analyze conjunctly ESM simulations and an ocean-only sensitivity experiment where open-ocean polynyas are artificially created by perturbing the Antarctic freshwater runoff. We find that enhanced CO2 outgassing takes place during the polynya opening, because old carbon-rich waters come in contact with the atmosphere. The concomitant increased uptake of anthropogenic CO2 partially compensates the CO2 outgassing. When the polynya closes, the ocean CO2 uptake increases significantly, possibly fueled by abundant nutrients and higher alkalinity brought to the surface during the previous convective phase. Our results suggest that open-ocean polynyas could have a significant impact on the Southern Ocean CO2 uptake and could thus modulate its decadal variability.&#160;

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Ecosystem dynamics based on plankton functional types for global ocean biogeochemistry models

Global Change Biology ◽

10.1111/j.1365-2486.2005.1004.x ◽

2005 ◽

Vol 0 (0) ◽

pp. 051013014052005-??? ◽

Cited By ~ 148

Author(s):

Corinne Le Quere ◽

Sandy P. Harrison ◽

I. Colin Prentice ◽

Erik T. Buitenhuis ◽

Olivier Aumont ◽

...

Keyword(s):

Ecosystem Dynamics ◽

Global Ocean ◽

Functional Types ◽

Ocean Biogeochemistry

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Strong sensitivity of Southern Ocean carbon uptake and nutrient cycling to wind stirring

Biogeosciences Discussions ◽

10.5194/bgd-10-15033-2013 ◽

2013 ◽

Vol 10 (9) ◽

pp. 15033-15076 ◽

Cited By ~ 1

Author(s):

K. B. Rodgers ◽

O. Aumont ◽

S. E. Mikaloff Fletcher ◽

Y. Plancherel ◽

L. Bopp ◽

...

Keyword(s):

Carbon Cycle ◽

Southern Ocean ◽

Ad Hoc ◽

Global Ocean ◽

Nutrient Concentrations ◽

Carbon Uptake ◽

Carbon Cycle Model ◽

Ocean Biogeochemistry ◽

Ocean Carbon ◽

The Impact

Abstract. Here we test the hypothesis that winds have an important role in determining the rate of exchange of CO2 between the atmosphere and ocean through wind stirring over the Southern Ocean. This is tested with a sensitivity study using an ad hoc parameterization of wind stirring in an ocean carbon cycle model. The objective is to identify the way in which perturbations to the vertical density structure of the planetary boundary in the ocean impacts the carbon cycle and ocean biogeochemistry. Wind stirring leads to reduced uptake of CO2 by the Southern Ocean over the period 2000–2006, with differences of order 0.9 Pg C yr−1 over the region south of 45° S. Wind stirring impacts not only the mean carbon uptake, but also the phasing of the seasonal cycle of carbon and other species associated with ocean biogeochemistry. Enhanced wind stirring delays the seasonal onset of stratification, and this has large impacts on both entrainment and the biological pump. It is also found that there is a strong sensitivity of nutrient concentrations exported in Subantarctic Mode Water (SAMW) to wind stirring. This finds expression not only locally over the Southern Ocean, but also over larger scales through the impact on advected nutrients. In summary, the large sensitivity identified with the ad hoc wind stirring parameterization offers support for the importance of wind stirring for global ocean biogeochemistry, through its impact over the Southern Ocean.

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Vertical distribution of planktic foraminifera through an oxygen minimum zone: how assemblages and test morphology reflect oxygen concentrations

Biogeosciences ◽

10.5194/bg-18-977-2021 ◽

2021 ◽

Vol 18 (3) ◽

pp. 977-992

Author(s):

Catherine V. Davis ◽

Karen Wishner ◽

Willem Renema ◽

Pincelli M. Hull

Keyword(s):

Sediment Cores ◽

Biogeochemical Cycles ◽

Oxygen Minimum Zone ◽

Global Ocean ◽

Low Oxygen ◽

Planktic Foraminifera ◽

Morphometric Analyses ◽

Minimum Zone ◽

Global Biogeochemical Cycles ◽

Oxygen Minimum

Abstract. Oxygen-depleted regions of the global ocean are rapidly expanding, with important implications for global biogeochemical cycles. However, our ability to make projections about the future of oxygen in the ocean is limited by a lack of empirical data with which to test and constrain the behavior of global climatic and oceanographic models. We use depth-stratified plankton tows to demonstrate that some species of planktic foraminifera are adapted to life in the heart of the pelagic oxygen minimum zone (OMZ). In particular, we identify two species, Globorotaloides hexagonus and Hastigerina parapelagica, living within the eastern tropical North Pacific OMZ. The tests of the former are preserved in marine sediments and could be used to trace the extent and intensity of low-oxygen pelagic habitats in the fossil record. Additional morphometric analyses of G. hexagonus show that tests found in the lowest oxygen environments are larger, more porous, less dense, and have more chambers in the final whorl. The association of this species with the OMZ and the apparent plasticity of its test in response to ambient oxygenation invites the use of G. hexagonus tests in sediment cores as potential proxies for both the presence and intensity of overlying OMZs.

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