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Physics vs. biology in Southern Ocean nutrient gradients

Posted by mmaheigan

· Tuesday, June 16th, 2020

In the Southern Ocean, surface water silicate (SiO₄) concentrations decline very quickly relative to nitrate concentrations along a northward gradient toward mode water formation regions on the northern edge (Figure 1a, b). These mode waters play a critical role in driving global nutrient concentrations, setting the biogeochemistry of low- and mid-latitude regions around the globe after they upwell further north. To explain this latitudinal surface gradient, most hypotheses have implicated diatoms, which take up and export silicon as well as nitrogen: (1) Diatoms, including highly-silicified species such as Fragilariopsis kerguelensis, are more abundant in the Southern Ocean than elsewhere; (2) Iron limitation, which is prevalent in the Southern Ocean, elevates the Si:N ratio of diatoms; (3) Mass export of empty diatom frustules pumps silicate but not nitrate to deeper waters.

Figure 1: (a) and (b) nitrate and silicate concentrations in surface waters of the Southern Ocean (GLODAPv2_2019 data). (c) Model results of a standard run (black diamonds), a run without biology (red diamonds) and a run without mixing (blue diamonds).

In a recent paper published in Biogeosciences, the authors use an idealized model to explore the relative roles of biological vs. physical processes in driving the observed latitudinal surface nutrient gradients. Over timescales of a few years, removing the effects of biology (no SiO₄uptake or export) from the model elevates silicate concentrations slightly over the entire latitudinal range, but does not remove the strong latitudinal gradient (Figure 1c). However, if the effects of vertical mixing processes such as upwelling and entrainment are removed from the model by eliminating the observed deep [SiO₄] gradient, the observed surface nutrient gradient is greatly altered (Figure 1c). These model results suggest that, over short timescales, physics is more important than biology in driving the observed surface water gradient in SiO₄:NO₃ ratios and forcing silicate depletion of mode waters leaving the Southern Ocean. These findings add to our understanding of Southern Ocean dynamics and the downstream effects on other oceans.

Authors:
P. Demuynck (University of Southampton)
T. Tyrrell (University of Southampton)
A.C. Naveira Garabato (University of Southampton)
C.M. Moore (University of Southampton)
A.P. Martin (National Oceanography Centre)

A Methane-Charged Carbon Pump in Shallow Marine Sediments

Posted by mmaheigan

· Wednesday, June 3rd, 2020

Ocean margins are often characterized by the transport of methane, a potent greenhouse gas, entering from the subsurface and moving towards the seafloor. However, a significant portion of subsurface methane is consumed within shallow sediments via microbial driven anaerobic oxidation of methane (AOM). AOM converts the methane carbon to dissolved inorganic carbon (DIC) and reduces the amount of sulfate that diffuses down from the seafloor towards a sediment interval known as the sulfate-methane transition zone (SMTZ). The SMTZ is where the upward flux of methane encounters the downward diffusive sulfate flux (Figure 1). While the mechanisms of methane production and consumption have been extensively studied, the fate of the DIC that is produced in methane-charged sediments is not well constrained.

In a recent study published in Frontiers in Marine Science, authors used existing reports of methane and sulfate flux values to the SMTZ and synthesized a carbon flow model to quantify the DIC cycling in diffusive methane flux sites globally. They report an annual average of 8.7 Tmol (1 Tmol = 10¹² moles) of DIC entering the diffusive methane-charged shallow marine sediments due to sulfate reduction coupled with AOM and organic matter degradation, as well as DIC input from depth (Figure 1). Approximately 75% (average of 6.5 Tmol year^–1) of this DIC pool flows upward toward the water column, making it a potential contributor to oceanic CO₂and ocean acidification. Further, an average of 1.7 Tmol year^–1DIC precipitates as methane-derived authigenic carbonates. This synthesis emphasizes the importance of the SMTZ, not only as a methane sink but also an important biogeochemical front for global DIC cycling.

Figure 1: A simplified representation of DIC cycling at diffusive methane charged settings.

The study highlights that regions characterized by diffusive methane fluxes can contribute significantly to the oceanic inorganic carbon pool and sedimentary carbonate accumulation. DIC outflux from the methane-charged sediments is comparable to ~20% global riverine DIC flux to oceans. Methane-derived authigenic carbonate precipitation is comparable to ~15% of carbonate accumulation on continental shelves and in pelagic sediments, respectively. These pathways must be included in coastal and geologic carbon models.

Authors:
Sajjad Akam (Texas A&M University-Corpus Christi)
Richard Coffin (Texas A&M University-Corpus Christi)
Hussain Abdulla (Texas A&M University-Corpus Christi)
Timothy Lyons (University of California, Riverside)

Little big exporters

Posted by mmaheigan

· Wednesday, April 8th, 2020

In the Southern Ocean, coccolithophores are thought to account for a major fraction of marine carbonate production and export to the deep sea. Despite their importance in the ocean carbon cycle, we lack fundamental information about Southern Ocean coccolithophore abundance, species composition, and contribution to carbonate export.

Figure caption: Heliscosphaera carteri (left), Coccolithus pelagicus (right) and Emiliania huxleyi (bottom right, partially behind C. pelagicus) coccospheres retrieved from the subantarctic waters south of Tasmania. Image Ruth Eriksen, courtesy AAD EMU.

A recent study in Biogeosciences has generated annual observations of coccolithophore species composition and contribution to calcium carbonate fluxes at two sites that are representative of a large portion of the Subantarctic zone. Coccolithophores account for roughly half of the annual calcium carbonate exported to the deep sea. Notably, it is not the most abundant species (Emiliania huxleyi), but rather the less abundant and larger species (e.g. Calcidiscus leptoporus, Helicosphaera carteri and Coccolithus pelagicus) that make the greatest contribution to carbonate export to the deep sea. Since these larger species exhibit substantially different ecological traits from the opportunistic E. huxleyi, predictions of future response of Southern Ocean coccolithophore communities should not be based on the physiological results from experiments with E. huxleyi. Rather, new physiological response experiments of those less abundant, larger coccolithophore species are urgently needed to constrain responses of these important carbonate exporters to environmental change in the Southern Ocean. This study underscores the importance of phytoplankton ecological traits on the regulation of the marine carbon cycle and emphasizes the need for more species-specific studies to improve predictions of marine ecosystem response to ongoing climate change.

Authors
Andrés S. Rigual Hernández (Universidad de Salamanca)
Thomas W. Trull (CSIRO and ACE CRC)
Scott D. Nodder (NIWA)
José A. Flores (Universidad de Salamanca)
Helen Bostock (University of Queensland,)
Fátima Abrantes (Portuguese Institute for Sea and Atmosphere and CCMAR)
Ruth S. Eriksen (CSIRO and IMAS)
Francisco J. Sierro (Universidad de Salamanca)
Diana M. Davies (CSIRO and ACE CRC)
Anne-Marie Ballegeer (Universidad de Salamanca)
Miguel A. Fuertes (Universidad de Salamanca)
Lisa C. Northcote (NIWA)

Tiny, but effective: Gelatinous zooplankton and the ocean biological carbon pump

Posted by mmaheigan

· Wednesday, March 25th, 2020

Barely visible to the naked eye, gelatinous zooplankton play important roles in marine food webs. Cnidaria, Ctenophora, and Urochordata are omnipresent and provide important food sources for many more highly developed marine organisms. These small, nearly transparent organisms also transport large quantities of “jelly-carbon” from the upper ocean to depth. A recent study in Global Biogeochemical Cycles focused on quantifying the gelatinous zooplankton contribution to the ocean carbon cycle.

Figure 1. Processes and pathways or gelatinous carbon transfer to the deep ocean.

Using >90,000 data points (1934 to 2011) from the Jellyfish Database Initiative (JeDI), the authors compiled global estimates of jellyfish biomass, production, vertical migration, and jelly carbon transfer efficiency. Despite their small biomass relative to the total mass of organisms living in the upper ocean, their rapid, highly efficient sinking makes them a globally significant source of organic carbon for deep-ocean ecosystems, with 43-48% of their upper ocean production reaching 2000 m, which translates into 0.016 Pg C yr^-1.

Figure 2. Mass deposition event of jellyfish at 3500 m in the Arabian Sea (Billett et al. 2006).

Sediment trap data have suggested that carbon transport associated with large, episodic gelatinous blooms in localized open ocean and continental shelf regions could often exceed phytodetrital sources, in particular instances. These mass deposition events and their contributions to deep carbon export must be taken into account in models to better characterize marine ecosystems and reduce uncertainties in our understanding of the ocean’s role in the global carbon cycle.

Links:

Jellyfish Database Initiative http://jedi.nceas.ucsb.edu, http://jedi.nceas.ucsb.edu-dmo.org/dataset/526852 )

Authors:
Mario Lebrato (Christian‐Albrechts‐University Kiel and Bazaruto Center for Scientific Studies, Mozambique)
Markus Pahlow (GEOMAR)
Jessica R. Frost (South Florida Water Management District)
Marie Küter (Christian‐Albrechts‐University Kiel)
Pedro de Jesus Mendes (Marine and Environmental Scientific and Technological Solutions, Germany)
Juan‐Carlos Molinero (GEOMAR)
Andreas Oschlies (GEOMAR)

Hurricane-driven surge of labile carbon into the deep North Atlantic Ocean

Posted by mmaheigan

· Thursday, February 27th, 2020

Tropical cyclones (hurricanes and typhoons) are the most extreme episodic weather event affecting subtropical and temperate oceans. Hurricanes generate intense surface cooling and vertical mixing in the upper ocean, resulting in nutrient upwelling into the photic zone and episodic phytoplankton blooms. However, their influence on the deep ocean is unknown.

Figure 1. (a) Particulate organic carbon (POC) flux and percentage of the total mass flux (yellow) (top panel); fluxes (middle panel) and POC-normalized concentrations (bottom panel) of diagnostic lipid biomarkers for phytoplankton-derived and labile material, zooplankton, bacteria, and other (see legend); (b) Lipid concentrations (left panel) and POC-normalized concentrations (right panel) of diagnostic lipid biomarkers for the same sources as in (a) (see legend) measured two weeks after Nicole’s passage (25-29 Oct. 2016). Shown for reference are total lipid concentration profiles in April 2015 (dark gray, typical post spring bloom conditions) and Nov 2015 (light gray, typical minimum production period).

In October 2016, Category 3 Hurricane Nicole passed over the Bermuda time-series site (Oceanic Flux Program (OFP) and Bermuda Atlantic Time-Series site (BATS)) in the oligotrophic NW Atlantic Ocean. In a recent study published in Geophysical Research Letters, authors synthesized multidisciplinary data from hydrographic and phytoplankton measurements and lipid composition of sinking and suspended particles collected from OFP and BATS, respectively, after Hurricane Nicole in 2016. After the hurricane passed, particulate fluxes of lipids diagnostic of fresh phytodetritus, zooplankton, and microbial biomass increased by 30-300% at 1500 m depth and 30-800% at 3200 m depth (Figure 1a). In addition, mesopelagic suspended particles were enriched in phytodetrital material, as well as zooplankton- and bacteria-sourced lipids (Figure 1b), indicating particle disaggregation and a deep-water ecosystem response.

These results suggest that carbon export and biogeochemical cycles may be impacted by climate-induced changes in hurricane frequency, intensity, and tracks, and, underscore the sensitivity of deep ocean ecosystems to climate perturbations.

Authors:
Rut Pedrosa-Pamies (Marine Biological Laboratory)
Maureen H. Conte (Bermuda Institute of Ocean Science and Marine Biological Laboratory)
JC Weber (Marine Biological Laboratory)
Rodney Johnson (Bermuda Institute of Ocean Science)

Unexpected DOC additions in the deep Atlantic

Posted by mmaheigan

· Tuesday, January 7th, 2020

Oceanic dissolved organic carbon (DOC) ultimately exchanges with atmospheric CO₂ and thus represents an important carbon source/sink with consequence for climate. Most of the DOC is recalcitrant to microbial degradation, with some fractions surviving for thousands of years. Therefore, DOC in the deep ocean was thought to be stable or to decrease slowly over decades to centuries due to biotic and abiotic sinks. However, a study published in Global Biogeochemical Cycles shows that there are some zones of the deep Atlantic Ocean where recalcitrant DOC experiences net production. Using data from oceanographic cruises across the Atlantic Ocean, the authors first identified the major water masses in the basin and the percentage of each in every sample taken for DOC analysis. The study revealed net additions of 27 million tons of dissolved organic carbon per year in the deep South Atlantic. On the other hand, the North Atlantic serves as a net sink, removing 298 million tons of carbon annually. DOC production observed in the deep Atlantic is probably due to the sinking particles that solubilize into DOC, since DOC enrichment was most evident at latitudes characterized as elevated productivity divergence zones.

Figure 1. Water masses along GO-SHIP line A16 (colored dots) and recalcitrant DOC variations due to biogeochemical processes (black dots within each water mass) in the deep Atlantic Ocean. Water mass domains are defined as the set of samples with the corresponding water mass proportion ≥50%. Recalcitrant DOC latitudinal variations per water stratum due to biogeochemical processes (ΔDOC) is in μmol kg^-1. Numbers on the plots are DOC values for the corresponding dots. Scales (not shown) are the same for all the plots, from -4 to 6 μmol kg^-1. Positive (negative) ΔDOC indicates values higher (lower) than the average DOC calculated for each water mass using an optimum multiparameter (OMP) analysis. DOC = dissolved organic carbon. AAIW = Antarctic Intermediate Water; UNADW = upper North Atlantic Deep Water; ISOW = Iceland Scotland Overflow Water; CDW = Circumpolar Deep Water; WSDW = Weddell Sea Deep Water. Figure created with Ocean Data View (Schlitzer, 2015).

Considering that the net DOC production over the entire Atlantic basin euphotic zone is 0.70–0.75 Pg C year^-1, the authors estimated that 30–39% of that DOC is consumed in the deep Atlantic subsequent to its export by overturning circulation. The upper North Atlantic Deep Water (UNADW) acts as the primary sink, accounting for 66% of the recalcitrant DOC removal in the North Atlantic. Conversely, the Antarctic Intermediate Water (AAIW) is the primary recipient, with 45% of recalcitrant DOC production in the South Atlantic, closely followed by the old UNADW that gains 44% of the recalcitrant DOC in the southern basin.

The Atlantic works as a mosaic of water masses, where both removal and addition of recalcitrant DOC occurs, with the dominant term dependent on the origin, temperature, age and depth of the water masses. The production of recalcitrant DOC in the deep ocean should be considered in biogeochemical models dealing with the carbon cycle and climate.

Authors:
C. Romera-Castillo and J. L. Pelegrí (Instituto de Ciencias del Mar, CSIC, Spain)
M. Álvarez (Instituto Español de Oceanografía, Spain)
D. A. Hansell (University of Miami, USA)
X. A. Álvarez-Salgado (Instituto de Investigaciones Marinas, CSIC, Spain)

What really controls deep-seafloor calcite dissolution?

Posted by mmaheigan

· Monday, December 16th, 2019

On time scales of tens to millions of years, seawater acidity is primarily controlled by biogenic calcite (CaCO₃) dissolution on the seafloor. Our quantitative understanding of future oceanic pH and carbonate system chemistry requires knowledge of what controls this dissolution. Past experiments on the dissolution rate of suspended calcite grains have consistently suggested a high-order, nonlinear dependence on undersaturation that is independent of fluid flow rate. This form of kinetics has been extensively adopted in models of deep-sea calcite dissolution and pH of benthic sediments. However, stirred-chamber and rotating-disc dissolution experiments have consistently demonstrated linear kinetics of dissolution and a strong dependence on fluid flow velocity. This experimental discrepancy surrounding the kinetic control of seafloor calcite dissolution precludes robust predictions of oceanic response to anthropogenic acidification.

In a recent study published in Geochimica et Cosmochimica Acta, authors have reconciled these divergent experimental results through an equation for the mass balance of the carbonate ion at the sediment-water interface (SWI), which equates the rate of production of that ion via dissolution and its diffusion in sediment porewaters to the transport across the diffusive sublayer (DBL) at the SWI. If the rate constant derived from suspended-grain experiments is inserted into this balance equation, the rate of carbonate ion supply to the SWI from the sediment (sediment-side control) is much greater in the oceans than the rate of transfer across the DBL (water-side control). Thus, calcite dissolution at the seafloor, while technically under mixed control, is strongly water-side dominated. Consequently, a model that neglects boundary-layer transport (sediment-side control alone) invariably predicts CaCO₃-versus-depth profiles that are too shallow compared to available data (Figure 1). These new findings will inform future attempts to model the ocean’s response to acidification.

Figure 1: Plots of the calcite (CaCO₃) content of deep-sea sediments as a function of oceanic depth. Left panel: data from the Northwestern Atlantic Ocean. Right panel: data from the Southwest Pacific Ocean. The blue line represents predicted CaCO₃ content assuming no boundary-layer effects (pure sediment-side control). The red line is the prediction that includes both sediment and water effects (mixed control), and the green line is the prediction with pure water-side control. The agreement between the red and green lines signifies that calcite dissolution is essentially water-side controlled at the seafloor. These results are duplicated for all tested regions of the oceans.

Authors:
Bernard P. Boudreau (Dalhousie University)
Olivier Sulpis (University of Utrecht)
Alfonso Mucci (McGill University)

Phytoplankton bloom from molten lava

Posted by mmaheigan

· Wednesday, September 18th, 2019

During June-August 2018, the oligotrophic North Pacific Ocean received an enormous quantity of nutrients in the form of molten lava, delivered by the erupting Kilauea on the big island of Hawaii. A phytoplankton bloom formed in response to the input of lava and an expedition was rapidly mobilized to determine its composition and the relevant biogeochemistry. We found that in addition to the nutrients derived from lava, exogenous nitrate was also present in the surface waters. Remotely operated vehicle observations in September 2019 by scientists at the Woods Hole Oceanographic Institution showed that lava from the 2018 eruption had reached depths of 700 m. Therefore, enabled by the intensity of the eruption and the island’s steep bathymetry, lava flows were able to extend below the thermocline and penetrate into nitrate-rich waters. Based on isotopic signatures of nitrate in the bloom, we inferred that heating of deep ocean waters resulted in the formation of buoyant seawater plumes, which rose to the sea surface. The rapid response expedition in July 2018 provided a unique opportunity to see first-hand how a massive input of exogenous nutrients alters marine ecosystems attuned to oligotrophic conditions.

Read more:
Ducklow, H. and T. Plank (06 Sep 2019) Volcano-stimulated marine photosynthesis. Science. Vol. 365, Issue 6457, pp. 978-979
DOI: 10.1126/science.aay8088>

Wilson, S. et al. (06 Sep 2019) Kīlauea lava fuels phytoplankton bloom in the North Pacific Ocean. Science Vol. 365, Issue 6457, pp.1040-1044
DOI: 10.1126/science.aax4767

Northeast Pacific time-series reveals episodic events as major player in carbon export

Posted by mmaheigan

· Tuesday, April 16th, 2019

Temporal fluctuations in the oceanic carbon budget play an important role in the cycling of organic matter from production in surface waters to consumption and sequestration in the deep ocean. A 29-year time-series (1989-2017) of particulate organic carbon (POC) fluxes and seafloor measurements of oxygen consumption in the abyssal northeast Pacific (Sta. M, 4,000 m depth) recently revealed an increasing proportional contribution from episodic events over the past seven years. From 2011 to 2017, 43% of POC flux arrived during high-magnitude (≥ mean + 2 σ) episodic events. Time lags between changes in satellite-estimated export flux (EF), POC flux to the seafloor, and seafloor oxygen consumption varied from 0 to 70 days among six flux events, which could be attributed to variable remineralization rates and/or particle sinking speeds. The Martin equation, a commonly used model to estimate carbon flux, predicted background fluxes well but missed episodic fluxes, subsequently underestimating the measured fluxes by almost 50% (Figure 1). This study reveals the potential importance of episodic POC pulses into the deep sea in the oceanic carbon budget, which has implications for observing infrastructure, model development, and field campaigns focused on quantifying carbon export.

Figure Caption: (A) Station M POC flux measured from sediment traps compared to Martin model estimates, from 1989 to 2017. (B) Model performance for years with >50% sampling coverage: (POC flux_Martin − POC flux_trap)/POC flux_trap 100.

Authors:
Kenneth Smith (MBARI)
Henry Ruhl (MBARI, NOC)
Christine Huffard (MBARI)
Monique Messié (MBARI, Aix Marseille Université)
Mati Kahru (Scripps)

Building ocean biogeochemistry observing capacity, one float at a time: An update on the Biogeochemical-Argo Program

Posted by mmaheigan

· Thursday, July 5th, 2018

By Ken Johnson (MBARI)

The Biogeochemical-Argo (BGC-Argo) Program is an international effort to develop a global network of biogeochemical sensors on Argo profiling floats that has emerged from over a decade of community discussion and planning. While there is no formal funding for this global program, it is being implemented via a series of international research projects that harness the unique capabilities provided by BGC profiling floats. The U.S. Ocean Carbon and Biogeochemistry (OCB) Program maintains and supports a U.S. BGC-Argo subcommittee as a focal point for U.S. community input on the implementation of the global biogeochemical float array and associated science program development.

Figure 1. Steve Riser deploying a SOCCOM float from the R/V Palmer

About BGC-Argo Floats
BGC-Argo floats can carry a suite of chemical and bio-optical sensors (Figure 1 – Float Schematic). They have enough energy to make about 250 to 300 vertical profiles from 2000 m to the surface. At a cycle time of 10 days, that corresponds to a lifetime near 7 years. The long endurance allows the floats to resolve seasonal to interannual variations in carbon and nutrient cycling throughout the water column. These time scales are difficult to study from ships and ocean interior processes are hard to resolve from satellites. BGC profiling floats extend the capabilities of these traditional observing systems in significant ways.

Figure 2. Images of Navis and APEX floats used in the SOCCOM program. These floats carry oxygen, nitrate, pH, and bio-optical (chlorophyll fluorescence and backscatter) sensors.

All of the data from profiling floats operating as part of the Argo program must be available in real-time with no restrictions on access. The Argo Global Data Assembly centers in France and the USA both provide complete listings of all BGC profiles (argo_bio-profile_index.txt) and access to the data. Extensive documentation of the data processing protocols is available from the Argo Data Management Team. Individual research programs, such as SOCCOM (see below), may also provide direct data access to the observed data along with value added products such as best estimates of pCO₂ derived from pH sensor data.

Regional Deployments
In 2018, it is projected that 127 profiling floats with biogeochemical sensors are will be deployed, including ~40 floats by U.S. projects. Most of the U.S. deployments (30+) will be carried out by the Southern Ocean Carbon and Climate Observations and Modeling (SOCCOM) project (Figure 2 – Float Deployment). These floats will carry oxygen, nitrate, pH, chlorophyll fluorescence, and backscatter sensors. As part of the NOAA Tropical Pacific Observing System (TPOS) program, Steve Riser’s group (Univ. Washington) will deploy 3 BGC-Argo floats per year in the equatorial Pacific over the next 4 years. These floats will be equipped with oxygen, pH, bio-optical sensors and Passive Acoustic Listener (PAL) sensors, which provide wind speed estimates at 15-minute intervals while the floats are parked at 1000 m. Wind speed is derived from the noise spectrum of breaking waves. Steve Emerson (Univ. Washington), with NSF support, is also deploying floats equipped with oxygen, nitrate and pH sensors in the equatorial Pacific. With funding from NSF, Andrea Fassbender (MBARI) will deploy two floats at Ocean Station Papa in the northeast Pacific in collaboration with the EXPORTS program. These floats will also carry oxygen, nitrate, pH, and bio-optical sensors.

Nearly 90 BGC floats will be deployed in 2018 by other nations in multiple ocean basins. Much of this effort will focus on the North Pacific and North Atlantic. The sensor load on these floats is somewhat variable. Some will be deployed with only oxygen sensors or bio-optical sensors for chlorophyll fluorescence and particle abundance. Others will carry the full suite of six sensors (oxygen, nitrate, pH, chlorophyll fluorescence, backscatter, and irradiance) that are outlined in the BGC-Argo Implementation Plan (BGC-Argo, 2016). These floats will contribute to the existing array of 305 biogeochemical floats (Figure 3 BGC Argo Map).

Community Activities
In response to the tremendous interest in the scientific community in the capabilities of profiling floats, OCB is sponsoring a Biogeochemical Float Workshop at the University of Washington in Seattle from July 9-13, 2018 to begin the process of transferring this expertise to the broader oceanographic community, bringing together potential users of this technology to discuss biogeochemical profiling float technology, sensors, and data management and begin the process of the intelligent design of future scientific experiments. The workshop will provide participating scientists direct access to the facilities of the Float Laboratory operated by Riser. This workshop builds on a previous OCB workshop Observing Biogeochemical Cycles at Global Scales with Profiling Floats and Gliders (Johnson et al., 2009). BGC-Argo will also have a prominent presence at the 6th Argo Science Workshop (October 22-24, 2018, Tokyo, Japan) and OceanObs19 (September 16-20, 2019, Honolulu, HI).

Figure 3. May 2018 map of the location of BGC-Argo floats that have reported in the previous month and sensor types on these floats. From jcommops.org.

BGC-Argo Publications
Several resources now highlight the capabilities of profiling floats to accomplish scientific observing goals. A web-based bibliography of biogeochemical float papers hosted on the Biogeochemical-Argo website currently includes >100 publications and continues to grow. A special issue of Journal of Geophysical Research: Oceans focused on the SOCCOM program is in progress with 11 papers now available and a dozen more forthcoming. These papers include summaries of the technical capabilities of floats and the biogeochemical sensors, comparisons of float bio-optical data with satellite remote sensing observations, seasonal and interannual assessments of air-sea oxygen flux, under-ice biogeochemistry, carbon export, comparisons of pCO₂ estimated from floats with pH vs. time-series data, and net community production. The connection of float observations with numerical models is a special focus of the program and this is highlighted in several papers, including a description of the Biogeochemical Southern Ocean State Estimate (SOSE), which is a data assimilating BGC model. Results from Observing System Simulation Experiments (OSSEs) used to assess the number of floats needed for large-scale observations are also reported. The BGC-Argo steering committee is developing a community white paper for the OceanObs19 conference in September 2019. BGC-Argo also develops and distributes a community newsletter.

For more information, visit the BGC-Argo website or reach out to the U.S. BGC-Argo Subcommittee.

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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