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

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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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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Stochastic Subgrid-Scale Ocean Mixing: Impacts on Low-Frequency Variability

Journal of Climate ◽

10.1175/jcli-d-16-0539.1 ◽

2017 ◽

Vol 30 (13) ◽

pp. 4997-5019 ◽

Cited By ~ 16

Author(s):

Stephan Juricke ◽

Tim N. Palmer ◽

Laure Zanna

Keyword(s):

Southern Ocean ◽

Interannual Variability ◽

Time Scales ◽

High Frequency ◽

Low Frequency ◽

Global Ocean ◽

Small Scale ◽

Subgrid Scale ◽

Low Frequency Variability ◽

Ocean Models

In global ocean models, the representation of small-scale, high-frequency processes considerably influences the large-scale oceanic circulation and its low-frequency variability. This study investigates the impact of stochastic perturbation schemes based on three different subgrid-scale parameterizations in multidecadal ocean-only simulations with the ocean model NEMO at 1° resolution. The three parameterizations are an enhanced vertical diffusion scheme for unstable stratification, the Gent–McWilliams (GM) scheme, and a turbulent kinetic energy mixing scheme, all commonly used in state-of-the-art ocean models. The focus here is on changes in interannual variability caused by the comparatively high-frequency stochastic perturbations with subseasonal decorrelation time scales. These perturbations lead to significant improvements in the representation of low-frequency variability in the ocean, with the stochastic GM scheme showing the strongest impact. Interannual variability of the Southern Ocean eddy and Eulerian streamfunctions is increased by an order of magnitude and by 20%, respectively. Interannual sea surface height variability is increased by about 20%–25% as well, especially in the Southern Ocean and in the Kuroshio region, consistent with a strong underestimation of interannual variability in the model when compared to reanalysis and altimetry observations. These results suggest that enhancing subgrid-scale variability in ocean models can improve model variability and potentially its response to forcing on much longer time scales, while also providing an estimate of model uncertainty.

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Transient Overturning Compensation between Atlantic and Indo-Pacific Basins

Journal of Physical Oceanography ◽

10.1175/jpo-d-20-0060.1 ◽

2020 ◽

Vol 50 (8) ◽

pp. 2151-2172 ◽

Cited By ~ 1

Author(s):

Shantong Sun ◽

Andrew F. Thompson ◽

Ian Eisenman

Keyword(s):

Southern Ocean ◽

Time Scales ◽

North Atlantic ◽

Climate Models ◽

Diffusion Processes ◽

Formation Rate ◽

Deep Ocean ◽

Meridional Overturning Circulation ◽

Global Ocean ◽

Overturning Circulation

AbstractClimate models consistently project (i) a decline in the formation of North Atlantic Deep Water (NADW) and (ii) a strengthening of the Southern Hemisphere westerly winds in response to anthropogenic greenhouse gas forcing. These two processes suggest potentially conflicting tendencies of the Atlantic meridional overturning circulation (AMOC): a weakening AMOC due to changes in the North Atlantic but a strengthening AMOC due to changes in the Southern Ocean. Here we focus on the transient evolution of the global ocean overturning circulation in response to a perturbation to the NADW formation rate. We propose that the adjustment of the Indo-Pacific overturning circulation is a critical component in mediating AMOC changes. Using a hierarchy of ocean and climate models, we show that the Indo-Pacific overturning circulation provides the first response to AMOC changes through wave processes, whereas the Southern Ocean overturning circulation responds on longer (centennial to millennial) time scales that are determined by eddy diffusion processes. Changes in the Indo-Pacific overturning circulation compensate AMOC changes, which allows the Southern Ocean overturning circulation to evolve independently of the AMOC, at least over time scales up to many decades. In a warming climate, the Indo-Pacific develops an overturning circulation anomaly associated with the weakening AMOC that is characterized by a northward transport close to the surface and a southward transport in the deep ocean, which could effectively redistribute heat between the basins. Our results highlight the importance of interbasin exchange in the response of the global ocean overturning circulation to a changing climate.

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Changes in the Antarctic sea ice ecosystem: potential effects on krill and baleen whales

Marine and Freshwater Research ◽

10.1071/mf07161 ◽

2008 ◽

Vol 59 (5) ◽

pp. 361 ◽

Cited By ~ 60

Author(s):

Stephen Nicol ◽

Anthony Worby ◽

Rebecca Leaper

Keyword(s):

Climate Change ◽

Southern Ocean ◽

Sea Ice ◽

Ocean Circulation ◽

Trophic Levels ◽

Global Ocean ◽

Ecological Change ◽

Cetacean Species ◽

Baleen Whales ◽

The Antarctic

The annual formation and loss of some 15 million km2 of sea ice around the Antarctic significantly affects global ocean circulation, particularly through the formation of dense bottom water. As one of the most profound seasonal changes on Earth, the formation and decay of sea ice plays a major role in climate processes. It is also likely to be impacted by climate change, potentially changing the productivity of the Antarctic region. The sea ice zone supports much wildlife, particularly large vertebrates such as seals, seabirds and whales, some exploited to near extinction. Cetacean species in the Southern Ocean will be directly impacted by changes in sea ice patterns as well as indirectly by changes in their principal prey, Antarctic krill, affected by modifications to their own environment through climate change. Understanding how climate change will affect species at all trophic levels in the Southern Ocean requires new approaches and integrated research programs. This review focuses on the current state of knowledge of the sea ice zone and examines the potential for climatic and ecological change in the region. In the context of changes already documented for seals and seabirds, it discusses potential effects on the most conspicuous vertebrate of the region, baleen whales.

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Productivity and Change in Fish and Squid in the Southern Ocean

Frontiers in Ecology and Evolution ◽

10.3389/fevo.2021.624918 ◽

2021 ◽

Vol 9 ◽

Author(s):

Jilda Alicia Caccavo ◽

Henrik Christiansen ◽

Andrew J. Constable ◽

Laura Ghigliotti ◽

Rowan Trebilco ◽

...

Keyword(s):

Climate Change ◽

Southern Ocean ◽

Life Histories ◽

Ross Sea ◽

Global Climate ◽

Management Strategies ◽

Antarctic Fish ◽

Ecosystem Approach ◽

Ecosystem Structure ◽

Global Drivers

Southern Ocean ecosystems are globally important and vulnerable to global drivers of change, yet they remain challenging to study. Fish and squid make up a significant portion of the biomass within the Southern Ocean, filling key roles in food webs from forage to mid-trophic species and top predators. They comprise a diverse array of species uniquely adapted to the extreme habitats of the region. Adaptations such as antifreeze glycoproteins, lipid-retention, extended larval phases, delayed senescence, and energy-conserving life strategies equip Antarctic fish and squid to withstand the dark winters and yearlong subzero temperatures experienced in much of the Southern Ocean. In addition to krill exploitation, the comparatively high commercial value of Antarctic fish, particularly the lucrative toothfish, drives fisheries interests, which has included illegal fishing. Uncertainty about the population dynamics of target species and ecosystem structure and function more broadly has necessitated a precautionary, ecosystem approach to managing these stocks and enabling the recovery of depleted species. Fisheries currently remain the major local driver of change in Southern Ocean fish productivity, but global climate change presents an even greater challenge to assessing future changes. Parts of the Southern Ocean are experiencing ocean-warming, such as the West Antarctic Peninsula, while other areas, such as the Ross Sea shelf, have undergone cooling in recent years. These trends are expected to result in a redistribution of species based on their tolerances to different temperature regimes. Climate variability may impair the migratory response of these species to environmental change, while imposing increased pressures on recruitment. Fisheries and climate change, coupled with related local and global drivers such as pollution and sea ice change, have the potential to produce synergistic impacts that compound the risks to Antarctic fish and squid species. The uncertainty surrounding how different species will respond to these challenges, given their varying life histories, environmental dependencies, and resiliencies, necessitates regular assessment to inform conservation and management decisions. Urgent attention is needed to determine whether the current management strategies are suitably precautionary to achieve conservation objectives in light of the impending changes to the ecosystem.

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A latitudinally banded phytoplankton response to 21st century climate change in the Southern Ocean across the CMIP5 model suite

Biogeosciences ◽

10.5194/bg-12-5715-2015 ◽

2015 ◽

Vol 12 (19) ◽

pp. 5715-5734 ◽

Cited By ~ 24

Author(s):

S. Leung ◽

A. Cabré ◽

I. Marinov

Keyword(s):

Climate Change ◽

Southern Ocean ◽

21St Century ◽

Light Availability ◽

Southern Annular Mode ◽

Global Ocean ◽

Cmip5 Models ◽

Phytoplankton Abundance ◽

Phytoplankton Productivity ◽

Carbon Cycles

Abstract. Changes in Southern Ocean (SO) phytoplankton distributions with future warming have the potential to significantly alter nutrient and carbon cycles as well as higher trophic level productivity both locally and throughout the global ocean. Here we investigate the response of SO phytoplankton productivity and biomass to 21st century climate change across the CMIP5 Earth System Model suite. The models predict a zonally banded pattern of phytoplankton abundance and production changes within four regions: the subtropical (~ 30 to 40° S), transitional (~ 40 to 50° S), subpolar (~ 50 to 65° S) and Antarctic (south of ~ 65° S) bands. We find that shifts in bottom-up variables (nitrate, iron and light availability) drive changes in phytoplankton abundance and production on not only interannual, but also decadal and 100-year timescales – the timescales most relevant to climate change. Spatial patterns in the modelled mechanisms driving these biomass trends qualitatively agree with recent observations, though longer-term records are needed to separate the effects of climate change from those of interannual variability. Because much past observational work has focused on understanding the effects of the Southern Annular Mode (SAM) on biology, future work should attempt to quantify the precise influence of an increasingly positive SAM on SO biology within the CMIP5 models. Continued long-term in situ and satellite measurements of SO biology are clearly needed to confirm model findings.

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A latitudinally-banded phytoplankton response to 21st century climate change in the Southern Ocean across the CMIP5 model suite

Biogeosciences Discussions ◽

10.5194/bgd-12-8157-2015 ◽

2015 ◽

Vol 12 (11) ◽

pp. 8157-8197

Author(s):

S. Leung ◽

A. Cabré ◽

I. Marinov

Keyword(s):

Climate Change ◽

Southern Ocean ◽

21St Century ◽

Light Availability ◽

Southern Annular Mode ◽

Global Ocean ◽

Cmip5 Models ◽

Phytoplankton Abundance ◽

Phytoplankton Productivity ◽

Carbon Cycles

Abstract. Changes in Southern Ocean (SO) phytoplankton distributions with future warming have the potential to significantly alter nutrient and carbon cycles as well as higher trophic level productivity both locally and throughout the global ocean. Here we investigate the response of SO phytoplankton productivity and biomass to 21st century climate change across the CMIP5 Earth System Model suite. The models predict a zonally-banded pattern of phytoplankton abundance and production changes within 4 regions: the subtropical (~30° S to 40° S), transitional (~40° S to 50° S), subpolar (~50° S to 65° S) and Antarctic (south of ~65° S) bands. We find that shifts in bottom-up variables (nitrate, iron, and light availability) drive changes in phytoplankton abundance and production on not only interannual, but also decadal and 100-year timescales: the timescales most relevant to climate change. Spatial patterns in the modeled mechanisms driving these biomass trends qualitatively agree with recent observations, though longer-term records are needed to separate the effects of climate change from those of interannual variability. Because much past observational work has focused on understanding the effects of the Southern Annular Mode (SAM) on biology, future work should attempt to quantify the precise influence of an increasingly positive SAM on SO biology within the CMIP5 models. Continued long-term in-situ and satellite measurements of SO biology are clearly needed to confirm model findings.

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

Biogeosciences Discussions ◽

10.5194/bgd-12-11935-2015 ◽

2015 ◽

Vol 12 (14) ◽

pp. 11935-11985 ◽

Cited By ~ 3

Author(s):

C. Le Quéré ◽

E. T. Buitenhuis ◽

R. Moriarty ◽

S. Alvain ◽

O. Aumont ◽

...

Keyword(s):

Southern Ocean ◽

Food Webs ◽

Phytoplankton Biomass ◽

Biogeochemical Cycles ◽

Ecosystem Dynamics ◽

Global Ocean ◽

Model Simulations ◽

Zooplankton Dynamics ◽

Ocean Biogeochemistry ◽

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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Antarctic Futures: An Assessment of Climate-Driven Changes in Ecosystem Structure, Function, and Service Provisioning in the Southern Ocean

Annual Review of Marine Science ◽

10.1146/annurev-marine-010419-011028 ◽

2020 ◽

Vol 12 (1) ◽

pp. 87-120 ◽

Cited By ~ 23

Author(s):

A.D. Rogers ◽

B.A.V. Frinault ◽

D.K.A. Barnes ◽

N.L. Bindoff ◽

R. Downie ◽

...

Keyword(s):

Climate Change ◽

Ecosystem Services ◽

Southern Ocean ◽

Stratospheric Ozone ◽

Marine Ecosystems ◽

Ecosystem Structure ◽

Negative Consequences ◽

Key Species ◽

Antarctic Marine ◽

Impacts Of Climate Change

In this article, we analyze the impacts of climate change on Antarctic marine ecosystems. Observations demonstrate large-scale changes in the physical variables and circulation of the Southern Ocean driven by warming, stratospheric ozone depletion, and a positive Southern Annular Mode. Alterations in the physical environment are driving change through all levels of Antarctic marine food webs, which differ regionally. The distributions of key species, such as Antarctic krill, are also changing. Differential responses among predators reflect differences in species ecology. The impacts of climate change on Antarctic biodiversity will likely vary for different communities and depend on species range. Coastal communities and those of sub-Antarctic islands, especially range-restricted endemic communities, will likely suffer the greatest negative consequences of climate change. Simultaneously, ecosystem services in the Southern Ocean will likely increase. Such decoupling of ecosystem services and endemic species will require consideration in the management of human activities such as fishing in Antarctic marine ecosystems.

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Multi-millennial legacy of climate change in marine plankton communities

10.5194/egusphere-egu2020-20597 ◽

2020 ◽

Author(s):

Anne Strack ◽

Lukas Jonkers ◽

Marina C. Rillo ◽

Helmut Hillebrand ◽

Michal Kucera

Keyword(s):

Climate Change ◽

Time Scales ◽

Community Change ◽

Marine Phytoplankton ◽

Global Ocean ◽

Last Deglaciation ◽

Compositional Change ◽

Climatic Forcing ◽

Data Set ◽

The Last Deglaciation

Understanding the response of marine ecosystems to climate change requires knowledge of processes that operate over long time scales. Over the last decades, abundant data have been generated on the change in the composition of marine microplankton assemblages across the last deglaciation. These data were used to reconstruct various aspects of the ocean and climate system during this climatic upheaval; however, their potential to evaluate biotic response to climatic forcing has been rarely explored. Here, we compiled records of plankton response to the last deglaciation covering the entire North Atlantic Ocean. The records comprise assemblage composition data of marine zooplankton (planktonic foraminifera) and phytoplankton (coccolithophores, diatoms and dinoflagellates) covering the last 24&#160;ka with a resolution of at least 1&#160;ka. The comparability of the data is ensured by using either published age models or a combination of radiocarbon ages and correlated oxygen isotope data. We use these records to first determine the shape of the major compositional change in each record by principle components analyses and quantification of compositional turnover. The mean global response of the plankton to the deglaciation was then evaluated by an Empirical Orthogonal Function analysis of the main biotic trends across all sites. A preliminary analysis was run solely on the zooplankton data set as the phytoplankton data set is still work in progress. We find that the dominant response of the zooplankton consists of synchronous unidirectional shifts initiated between 16-17&#160;ka&#160;BP, and progressing into the Holocene. When regressed on the global ocean temperature and CO2 trends, we can see a proportionate response to the forcing during the last glacial maximum, the deglaciation and the early Holocene. In contrast, the late Holocene is characterised by continued compositional change, which does not appear related to environmental forcing. We speculate that this decoupling indicates the existence of a multi-millennial delay in community change following the climatic forcing, likely due to biotic interactions acting on communities that have been newly assembled or geographically displaced due to abiotic forcing. We will present a similar analysis for marine phytoplankton and discuss the consequences of the observations for the understanding of community variability on millennial time scales.

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