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Archive for ocean carbon uptake and storage – Page 7

Zooplankton vertical migrations represent a significant source of carbon export in the ocean

Posted by mmaheigan

· Friday, March 15th, 2019

Huge numbers of tiny marine animals, known as zooplankton, migrate between the surface ocean and the twilight zone (200 – 1,000 m below the surface) everyday; it is the largest migration event anywhere on the planet. How much carbon do these animals transport with them and how much do they leave behind sequestered in the deep ocean? In a recent publication in Global Biogeochemical Cycles, Archibald et al. (2019) used a simple model to estimate the magnitude of carbon flux into the twilight zone from zooplankton vertical migrations and observed that it was a significant contributor to carbon export on a global scale. The study also revealed strong regional patterns in migration-mediated carbon flux, with the greatest impact on export occurring at subtropical latitudes (Figure 1).

Figure 1. Percent increase in the modeled carbon export flux out of the surface ocean as a result of zooplankton vertical migrations.

Migrating zooplankton also consume significant amounts of oxygen at depth, generating a local maximum in the oxygen utilization profile at depth within the migration layer. By including the effect of the metabolism of migrating zooplankton, the model is able to produce a more detailed picture of oxygen utilization over the twilight zone. The model in this study effectively simulates the complex phenomenon of zooplankton vertical migrations, providing a simple framework that will allow researchers to investigate how this key component of the global carbon cycle might change under future climatic conditions. For example, if increased stratification leads to a greater representation of small cells in phytoplankton communities, then zooplankton migration-mediated carbon export is expected to make up a proportionally larger fraction of the total carbon export flux.

Authors:
Kevin M. Archibald (Woods Hole Oceanographic Institution and Massachusetts Institute of Technology)
David A. Siegel (University of California, Santa Barbara)
Scott C. Doney (University of Virginia)

How fast are elements sinking in the ocean?

Posted by mmaheigan

· Tuesday, March 5th, 2019

The sinking of elements in the ocean influences many important processes such as deep ocean carbon storage and the availability of trace metals for phytoplankton. Previously, quantification of this sinking flux has been done using sediment trap deployments or tracer measurements of a particle-reactive radioisotope. Since sediment traps and each particular radioisotope each have caveats in how they quantify sinking flux, sinking particulate flux measurements, especially trace metal fluxes, are especially sparse, with relatively large uncertainties. For the first time ever, in the U.S. GEOTRACES North Atlantic campaign (GA03), four types of radioisotope data (thorium-234, polonium-210, thorium-228 and thorium-230) were measured, along with a periodic table’s worth of particulate elements that can be used to quantify sinking fluxes at locations with prior sediment trap studies, including the Ocean Flux Program (OFP), for comparison.

Sinking flux estimates of particulate organic carbon (POC) and particulate iron (pFe) derived using different methods, including the different radionuclides labelled and sediment traps from oceanic sites near Bermuda. These include the Bermuda-Atlantic Time-series site (BATS), the Ocean Flux Program site (OFP), and the Bermuda Rise (BaRFlux site). The GA03 and BaRFlux data represent observations from 2012 and 2013. The triangles and stars represent data from throughout the time-series observations of those sites.

In a new study published in Global Biogeochemical Cycles, a team of collaborators synthesized all of the radioisotope and particle composition measurements from the GA03 cruise, as well as results from a nearby study called BaRFlux, to constrain sinking fluxes of carbon and eight trace elements (P, Cd, Co, Cu, Mn, Al, Fe and thorium-232) throughout the North Atlantic Ocean. The five different methods for constraining flux (sediment traps plus the four radioisotope methods) agree encouragingly well given the independent uncertainties associated with each method. Additionally, since the four radioisotopes have a range in half-lives from days to thousands of years, the different methods can reconstruct particle fluxes throughout the water column, from the dynamic bloom-and-bust-like changes near the surface to the relatively slow, long-term sinking into the abyssal ocean. These fluxes will improve the understanding of the global budgets of carbon and trace elements. This study would not have been possible without the support of OCB and GEOTRACES who co-funded a synthesis workshop on biogeochemical cycling of trace elements at the Lamont-Doherty Earth Observatory in summer 2016.

Also see Eos highlight on this article

Authors:
Christopher T. Hayes (University of Southern Mississippi)
Erin E. Black (Woods Hole Oceanographic Institution, now at Dalhousie University)
Robert F. Anderson (Lamont-Doherty Earth Observatory of Columbia University)
Mark Baskaran (Wayne State University)
Ken O. Buesseler (Woods Hole Oceanographic Institution)
Matthew A. Charette (Woods Hole Oceanographic Institution)
Hai Cheng (Xi’an Jiaotong University and University of Minnesota)
Kirk Cochran (Stony Brook University)
Lawrence Edwards (University of Minnesota)
Patrick Fitzgerald (Stony Brook University)
Phoebe J. Lam (University of California Santa Cruz
Yanbin Lu (Earth Observatory of Singapore)
Stephanie O. Morris (Woods Hole Oceanographic institution)
Daniel C. Ohnemus (Bigelow Laboratory for Ocean Sciences, now at Skidaway Institute of Oceanography)
Frank J. Pavia (Lamont-Doherty Earth Observatory of Columbia University)
Gillian Stewart (Queens College, City University of New York)
Yi Tang (Queens College, City University of New York)

Gulf of Mexico: A blue carbon hotspot of mangroves, seagrass and marshes

Posted by mmaheigan

· Wednesday, February 20th, 2019

The Gulf of Mexico (GoM) is an important global hotspot that comprises over 2.1615 million hectares of blue carbon habitats, including mangroves, seagrasses, and salt marshes, which collectively store 480.5 Tg of organic carbon (C_org) just in the upper 1 meter of sediment. Some of these important areas of carbon sequestration are protected or conserved, but much of the area is vulnerable, as 69 million people (US and Mexico) live within 50 miles of these blue carbon habitats, so the potential for development and subsequent habitat loss is high. In a recent study published in Science of the Total Environment, the estuaries around the GoM were delineated to determine areal extent and associated carbon stocks for all three habitats.

Figure 1: Map of blue carbon extent and stock for six sub-regions in the Gulf of Mexico estuaries and the Florida Shelf. The areal extent in hectares (ha) and associated organic carbon (C_org) stock in Tg is listed for each blue carbon system (MN = mangroves, SG = seagrass, SM = saltmarsh) in each sub-region. The underlying blue carbon map shows the distribution of mangroves (red), saltmarsh (yellow), and seagrass (blue) (used with permission from Chmura and Short, 2015).

Of the GoM blue carbon systems studied, mangroves sequester the most carbon, storing nearly 200 Tg C_org over 650,482 ha (Figure 1). Seagrass is ubiquitous throughout the GoM basin, spanning over 1 million ha and storing 184 Tg C_org, Salt marshes, which are predominantly found in the northwestern quadrant of the GoM account for just under 100 Tg C_org. In addition to presenting these updated blue carbon stock estimates for the GoM, this study estimates anthropogenic impacts on GoM blue carbon storage and compares GoM vs. Atlantic shoreline blue carbon habitat stocks and extents.

Authors:
Anitra L. Thorhaug (Yale University)
Helen M. Poulos (Wesleyan University)
Jorge López-Portillo (Instituto de Ecología Mexico)
Jordan Barr (Elder Research)
Ana Laura Lara-Domínguez (Instituto de Ecología Mexico)
Tim C. Ku (Wesleyan University)
Graeme P.Berlyn (Yale University

Dust-borne iron in the Southern Ocean was more bioavailable during glacial periods

Posted by mmaheigan

· Wednesday, January 23rd, 2019

The Southern Ocean is iron (Fe)-limited, and increased fluxes of dust-borne Fe to the Southern Ocean during the Last Glacial Maximum (LGM) have been associated with phytoplankton growth and CO₂ drawdown. Dust contains different mixes of Fe-bearing minerals, depending on the source region. Fe(II) silicate minerals from physical weathering are more bioavailable than Fe(III) oxyhydroxide minerals from chemical weathering. The Fe(II) silicates are dominant in dust sources that have been weathered from bedrock by glaciers in Patagonia, but the impact of glacial activity on dust-borne Fe speciation (Fe oxidation state and mineral composition) and bioavailability over the last glacial cycle has not previously been quantified.

Figure 1. The fraction of Fe(II) in dust (Fe(II)/Fetotal, dominated by Fe(II) silicates, shown as blue dots connected with dotted lines on blue axes) in marine sediment cores from (A) the South Atlantic and (B) the South Pacific plotted with the total dust flux (grey lines on grey axes).

A recent study in PNAS reconstructs the speciation of dust-borne Fe over the last glacial cycle in South Atlantic and South Pacific marine sediment cores using Fe K-edge X-ray absorption spectroscopy. The authors observed that the highly bioavailable Fe(II) silicate content of dust-borne Fe is higher in both regions during cold glacial periods, suggesting that a given flux of Fe is more bioavailable in glacial versus interglacial periods (Figure 1). Therefore, all Fe cannot be considered equal in biogeochemical models working on glacial-interglacial timescales. The bioavailability of a given flux of Fe at the LGM was likely a dominant driver of phytoplankton growth, with more bioavailable Fe driving increased phytoplankton activity and associated atmospheric CO₂ drawdown and subsequent cooling. The observed association between glacial periods and increased Fe bioavailability in the Southern Ocean may indicate an important positive feedback mechanism between glacial activity and cold glacial temperatures through Fe speciation and the efficiency of the biological pump.

Paper link: https://doi.org/10.1073/pnas.1809755115

Authors:
Elizabeth M. Shoenfelt (Lamont-Doherty Earth Observatory, Columbia University)
Gisela Winckler (Lamont-Doherty Earth Observatory, Columbia University)
Frank Lamy (Alfred Wegener Institute, Helmholtz Centre for Polar and Marine Research)
Robert F. Anderson (Lamont-Doherty Earth Observatory, Columbia University)
Benjamin C. Bostick (Lamont-Doherty Earth Observatory, Columbia University)

The past, present, and future of artificial ocean iron fertilization experiments

Posted by mmaheigan

· Wednesday, January 23rd, 2019

Since the beginning of the industrial revolution, human activities have greatly increased atmospheric CO₂ concentrations, leading to global warming and indicating an urgent need to reduce global greenhouse gas emissions. The Martin (or iron) hypothesis suggests that ocean iron fertilization (OIF) could be a low-cost effective method for reducing atmospheric CO₂ levels by stimulating carbon sequestration via the biological pump in iron-limited, high-nutrient, low-chlorophyll (HNLC) ocean regions. Given increasing global political, social, and economic concerns associated with climate change, it is necessary to examine the validity and usefulness of artificial OIF (aOIF) experimentation as a geoengineering solution.

Figure 1. (a) Global annual distribution of surface chlorophyll concentrations (mg m^-3) with locations of 13 aOIF experiments. Maximum and initial values in (b) maximum quantum yield of photosynthesis (Fv/Fm ratios) and (c) chlorophyll-a concentrations (mg m^-3) during aOIF experiments. (d) Changes in primary productivity (ΔPP = [PP]_{post-fertilization (postf)} ‒ [PP]_{pre-fertilization (pref)}; mg C m^-2 d^-1). (e) Distributions of chlorophyll-a concentrations (mg m^-3) on day 24 after iron addition in the Southern Ocean iron experiment-north (SOFeX-N) from MODIS Terra Level-2 daily image and on day 20 in the SOFeX-south (SOFeX-S) from SeaWiFS Level-2 daily image (white dotted box indicates phytoplankton bloom during aOIF experiments). (f) Changes in nitrate concentrations (ΔNO₃^– = [NO₃^–]_postf ‒ [NO₃^–]_pref; μM). (g) Changes in partial pressure of CO₂ (ΔpCO₂ = [pCO₂]_postf ‒ [pCO₂]_pref; μatm). The color bar indicates changes in dissolved inorganic carbon (ΔDIC = [DIC]_postf ‒ [DIC]_pref; μM). The numbers on the X axis indicate the order of aOIF experiments as given in Figure 1a and are grouped according to ocean basins; Equatorial Pacific (EP) (yellow bar), Southern Ocean (SO) (blue bar), subarctic North Pacific (NP) (red bar), and subtropical North Atlantic (NA) (green bar).

A review paper published in Biogeosciences on aOIF experiments provides a thorough overview of 13 scientific artificial OIF experiments conducted in HNLC regions over the last 25 years. These aOIF experiments have demonstrated that iron addition stimulates substantial increases in phytoplankton biomass and primary production, resulting in drawdown of macro-nutrients and dissolved inorganic carbon (Figure 1). Many of the aOIF experiments have also precipitated community shifts from smaller (pico- and nano-) to larger (micro) phytoplankton. However, the impact on the net transfer of CO₂ from the atmosphere to below the winter mixed layer via the biological pump is not yet fully understood or quantified and appears to vary with environmental conditions, export flux measurement techniques, and other unknown factors. These results, including possible side effects, have been debated among those who support and oppose aOIF experimentation, and many questions remain about the effectiveness of scientific aOIF, possible side effects, and international aOIF law frameworks. Therefore, it is important to continue undertaking small-scale, scientifically controlled studies to better understand natural processes in the HNLC regions, assess the associated risks, and lay the groundwork for evaluating the potential effectiveness and impacts of large-scale aOIF as a geoengineering solution to anthropogenic climate change. Additionally, this paper suggests considerations for the design of future aOIF experiments to maximize the effectiveness of the technique and begin to answer open questions under international aOIF regulations.

Authors:
Joo-Eun Yoon (Incheon National University)
Il-Nam Kim (Incheon National University)
Alison M. Macdonald (Woods Hole Oceanographic Institution)

Constraints on glacial overturning circulation and export production lead to answers about the carbon cycle

Posted by mmaheigan

· Friday, January 4th, 2019

One of the biggest unsolved mysteries in climate science concerns the dynamics and feedbacks of the ice age carbon dioxide (CO₂) cycle.

At the height of the Pleistocene ice ages, the atmospheric CO₂ concentration was about 1/3 lower than during the warm interglacial periods. Most scientists think that the CO₂ that was missing from the atmosphere was in the deep ocean, but how and why remains unclear. In a study published in Earth and Planetary Science Letters, we compared different computer simulations of the ice age ocean with δ¹³C, radiocarbon (¹⁴C), and δ¹⁵N data from sea floor sediments.

We find that a weak and shallow Atlantic Meridional Overturning Circulation (6-9 Sv, or approximately half of today’s overturning rate) best reproduces the glacial sediment isotope data. Increasing the atmospheric soluble iron flux in the model’s Southern Ocean intensifies export production, carbon storage, and further improves agreement with glacial δ¹³C and δ¹⁵N reconstructions.

Figure Caption: Depth profiles of global mean δ13C, calculated using only grid boxes for which there exists Last Glacial Maximum data. Blue: Weak Atlantic circulation; Red: Strong Atlantic circulation; Green: Collapsed Atlantic circulation; Dashed: Extra iron in the Southern Ocean; Orange: Last Glacial Maximum Data.

Our best-fitting simulation (blue, dashed line in the figure) is a significant improvement over previous studies and suggests that both circulation and export production changes were necessary to maximize carbon storage in the glacial ocean. These findings provide an equilibrium glacial state, consistent with a combination of proxies, that can be used as a basis for simulations covering the last deglaciation time period. Understanding the different states that the global climate system can transit, and the characteristics of the transitions, is crucial to project possible outcomes of current climate change processes.

Authors:
Juan Muglia (Oregon State University)
Luke C. Skinner (Godwin Laboratory for Palaeoclimate Research, University of Cambridge)
Andreas Schmittner (Oregon State University)

Alternative particle formation pathways identified in the Equatorial Pacific’s biological pump

Posted by mmaheigan

· Tuesday, November 27th, 2018

The ocean is one of the largest sinks of atmospheric carbon dioxide (CO₂) on our planet, driven in part by CO₂uptake by phytoplankton in the upper ocean during photosynthesis. Eventually, a portion of the resulting organic carbon is transported to depth, where it is sequestered from the atmosphere for centuries or even millennia. Our current understanding of the biological pump is based on the export of organic material in the form of large, fast-sinking (hundreds of meters per day) particles. However, using lipids as biomarkers, a recent study from the Equatorial Pacific Ocean published in JGR Biogeosciences showed that fast-sinking particles are refractory and distinctly different from plankton in the mixed layer, whereas slow-sinking particles were more labile and had a more similar composition to mixed layer particles (Fig. 1).

Figure 1. Particle lipid compositions for different particle fractions: ML = homogenous mixed layer particles, SU = suspended, SS = slow-sinking, and FS = fast-sinking of a) labile compounds known as unsaturated fatty acids synthesized by phytoplankton that provide a lot of energy for heterotrophs and b) sterols, including cholesterol (dark blue), which can be a biomarker for heterotrophy. Mixed layer particles are the most labile, showing the least degree of heterotrophic reworking, as expected. However, fast-sinking particles are most dissimilar from those in the mixed layer, with only a small proportion of labile compounds and a high degree of heterotrophic reworking.

The authors proposed a slower, less efficient export pathway, by which phytoplankton initially aggregate to smaller, slower-sinking detrital particles and then gradually form highly degraded, larger particles that sink to depth. Since smaller particles are respired more rapidly than larger particles, the proportion of phytoplankton-captured atmospheric CO₂ being stored in the deep ocean is likely reduced, particularly in regions dominated by smaller phytoplankton such as the Equatorial Pacific. This study clearly demonstrates the need for improved representation of a wider range of particle dynamics in models of the ocean’s biological pump.

Authors:
E. L. Cavan (University of Tasmania, previously University of Southampton)
S. Giering (National Oceanography Centre)
G. Wolff (University of Liverpool)
M. Trimmer (Queen Mary University London)
R. Sanders (National Oceanography Centre)

Artificial light from sampling platforms changes zooplankton behavior

Posted by mmaheigan

· Monday, November 26th, 2018

When designing sampling we make generally accepted assumptions that what we collect is representative of what is “normal” or naturally occurring at the place, time, and depth of collection. However, a recent study in Science Advances revealed that this might not be true. During round-the-clock shipboard sampling, lights used at night can actually be a form of pollution that disrupts the diel cycle of zooplankton vertical migration.

Effect of light pollution on krill from a ship (left), diel vertical migration in natural dark conditions (middle) and effect of moonlight (right). Figure by Malin Daase (UiT).

Using a Autonomous Surface Vehicle the authors documented zooplankton behavioral patterns of light avoidance never previously seen. The study compared results from high Arctic polar night (unpolluted light environment for an extended time), to near ship samples. During months of near constant darkness in the Arctic, there was still a diel vertical migration of zooplankton limited to the upper 30 m of the water column and centered around the local sun noon. Contrasting the results from light-polluted and unpolluted areas, the authors observed that the vast majority of the pelagic community exhibit a strong light-escape response in the presence of artificial light (both ship light and even headlamps from researchers in open boats). This effect was observed down to 100 m depth and 190 m from the ship. These results suggest that artificial light from traditional sampling platforms may bias studies of zooplankton abundance and diel migration within the upper 100 m. These findings underscore the need for alternative sampling methods such as autonomous platforms, particularly in dim-light conditions, to collect more accurate and representative physical and biological data for ecological studies. In addition to research cruises and sampling, anthropogenic light pollution from predicted increases in shipping, oil and gas exploration, and light-fishing are anticipated to impact the diel rhythms of zooplankton behavior all around the globe.

Authors:
Jørgen Berge (Norwegian University of Technology and Science; UiT The Arctic University of Norway)
Martin Ludvigsen (Norwegian University of Technology and Science; University Centre in Svalbard)
Maxime Geoffroy (UiT The Arctic University of Norway, Memorial University of Newfoundland)
Jonathan H. Cohen (University of Delaware)
Pedro R. De La Torre (Norwegian University of Technology and Science)
Stein M. Nornes (Norwegian University of Technology and Science)
Hanumant Singh (Northeastern University)
Asgeir J. Sørensen (Norwegian University of Technology and Science)
Malin Daase (Norwegian University of Technology and Science)
Geir Johnsen (Norwegian University of Technology and Science; Norwegian University of Technology and Science)

Efficient carbon drawdown allows for a high future carbon uptake in the North Atlantic

Posted by mmaheigan

· Wednesday, November 7th, 2018

As one of the major carbon sinks in the global ocean, the North Atlantic is a key player in mediating and ameliorating the ongoing global warming. Current projections of the North Atlantic carbon sink in a high-CO₂ future vary greatly among models, with some showing that a slowdown in carbon uptake has already begun and others predicting that this slowdown will not occur until nearly 2100. To ensure the credibility of future projections as needed for finding adequate mitigation strategies, it is important to address and reduce this uncertainty.

Percentage of anthropogenically altered carbon stored in the deep North Atlantic (left panel) and North Atlantic uptake of anthropogenically altered carbon (right panel) as simulated by 11 different Earth System Models for a high CO2-future. Black x and line in left panel mark the observational estimate and its uncertainties, while blue and red shading reflect model spread, including models that simulate deep ocean storage within (blue) and outside (red) these observational uncertainties.

A new study in the Journal of Climate identified some of the mechanisms behind this ambiguity by analyzing the output of 11 Earth System Models for a high-CO₂ future. The authors show that discrepancies among models largely originate around high-latitude gateways from the surface to the deep ocean. Through biological production, deep convection and subsequent transport via the deep western boundary current, these gateways remove carbon from the upper ocean. When enough carbon is removed to maintain a lower oceanic pCO₂ relative to atmospheric pCO₂, the ocean continues to take up carbon. The study reveals that the fraction of anthropogenic carbon that is stored below 1000 m depth is not only an indicator of current carbon removal from the upper ocean but also a predictor of future ocean carbon uptake. When models that lie outside the range of observational uncertainties in deep carbon storage (red shading, left panel of figure) were excluded, revised projections showed higher North Atlantic carbon uptake in the future with lower associated uncertainties (blue shading, right panel of figure). This result highlights the need to depart from the concept of more or less randomly chosen models when reporting on future projections and their uncertainties. Results that are more reliable and hence of better use for mitigation strategies can be gained by focusing solely on models that simulate key mechanisms within observational uncertainties.

Authors:
N. Goris (Bjerknes Centre for Climate Research, Norway)
J.F. Tjiputra (Bjerknes Centre for Climate Research, Norway)
A. Olsen (University of Bergen and Bjerknes Centre for Climate Research, Norway)
J. Schwinger (Bjerknes Centre for Climate Research, Norway)
S.K. Lauvset (Bjerknes Centre for Climate Research, Norway)
E. Jeansson (Bjerknes Centre for Climate Research, Norway)

Investigating variability and change in subpolar Southern Ocean pCO2 via time-series and float data

Posted by mmaheigan

· Tuesday, November 6th, 2018

The Southern Ocean dominates the mean global ocean sink for anthropogenic carbon, but its sparse sampling relative to other basins limits our capacity to quantify carbon uptake and accompanying seasonal to interannual variability, which is critical to predicting future ocean carbon uptake and storage. Since 2002, underway pCO₂measurements collected as part of the Drake Passage Time-series (DPT) Program have informed our understanding of seasonally varying air-sea pCO₂gradients and by inference, the carbon fluxes in this region. Understanding whether Drake Passage air-sea fluxes are representative of the broader subpolar Southern Ocean was the focus of a recent study in Biogeosciences.

Top left panel: Mean surface ocean seasonal pCO2 cycle estimate for datasets from the Surface Ocean CO2 Atlas (SOCAT) in the subpolar Southern Ocean: black- SOCAT within the Drake Passage (DP) region; green- SOCAT outside the DP region; blue- all SOCAT in Southern Ocean Subpolar Seasonally Stratified (SPSS) biome; red- Self Organizing Map Feed-forward Network (SOM-FFN) product. Shading represents 1 standard error for biome-scale monthly means driven by interannual variability. Bar plot indicates the number of years containing observations in a given month (maximum of 15 years).
Top right panel: Mean surface ocean pCO2 seasonal cycle estimate for black: underway Drake Passage Time-series data for years 2002–2016; purple: DPT for years 2016–2017 to match years covered by the floats; and orange: SOCCOM floats. Seasonal cycles are shown on an 18-month cycle, calculated from a monthly mean time series with the atmospheric correction to year 2017. Shading represents 1 standard error accounting for the spatial and temporal heterogeneity of the sample and the measurement error (2.7 % or ±11 µatm at a pCO2 of 400 µatm for floats; ±2 µatm for DPT data) combined using the square root of the sum of squares.

An analysis of available Southern Ocean pCO₂ data from inside vs. outside the Drake Passage showed agreement in the timing and amplitude of seasonal pCO₂ variations, suggesting that the seasonality so carefully recorded by DPT is in fact representative of the broader subpolar Southern Ocean. DPT’s high temporal resolution sampling is critical to constraining estimates of the seasonal cycle of surface pCO₂ in this region, as wintertime underway pCO₂ data remain sparse outside the Drake Passage. Comparisons of the DPT data to an emerging dataset of float-estimated pCO₂ from the SOCCOM (Southern Ocean Carbon and Climate Observations and Modeling) project showed that both shipboard and autonomous platforms capture the expected seasonal cycle for the subpolar Southern Ocean, with an austral wintertime peak driven by deep mixing and a summertime low driven by biological uptake. However, the seasonal cycle derived from float-estimated pCO₂ has a larger seasonal amplitude compared to the DPT data due to an earlier and much lower observed summertime minimum.

The Drake Passage Time-series illustrates the large variability of surface ocean pCO₂ in the Southern Ocean and exemplifies the value of sustained observations for understanding changing ocean carbon uptake in this dynamic region. Coordinated monitoring efforts that combine a robust ship-based observational network with a well-calibrated array of autonomous biogeochemical floats will improve and expand our understanding of the Southern Ocean carbon cycle in the future.

Authors:
Amanda R. Fay (Lamont Doherty Earth Observatory)
Nicole S. Lovenduski (University of Colorado)
Galen A. McKinley (Lamont Doherty Earth Observatory)
David R. Munro (University of Colorado)
Colm Sweeney (University of Colorado, NOAA Earth System Research Laboratory)
Alison R. Gray (University of Washington)
Peter Landschützer (Max Planck Institute for Meteorology, Germany)
Britton B. Stephens (National Center for Atmospheric Research)
Taro Takahashi (Lamont Doherty Earth Observatory)
Nancy Williams (Oregon State University)

Funding for the Ocean Carbon & Biogeochemistry Project Office is provided by the National Science Foundation (NSF) and the National Aeronautics and Space Administration (NASA). The OCB Project Office is housed at the Woods Hole Oceanographic Institution.

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