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Ocean iron fertilization may amplify pressures on marine biomass with only a limited climate benefit

Posted by hbenway

· Friday, January 26th, 2024

Amidst a heightened focus on the need for both drastic and immediate emissions reductions and carbon dioxide removal to limit warming to 1.5°C (IPCC, 2022), attention is returning to ocean iron fertilization (OIF) as a means of marine carbon dioxide removal (mCDR). First discussed in the early 1990s by John Martin, the concept posits that fertilization of iron-limited marine phytoplankton would lead to enhanced ocean carbon storage via a stimulation of the ocean’s biological carbon pump. However, we lack knowledge about how OIF might operate in concert with an ocean responding to climate change and what the consequences of altered nutrient consumption patterns might be for marine ecosystems, particularly for fisheries in national exclusive economic zones (EEZs). Tagliabue et al. (2023) addressed this in a recent study using state-of-the-art climate, ocean biogeochemical, and ecosystem models under a high-emissions scenario.

The study’s findings suggested that OIF can contribute at most a few 10s of Pg of mCDR under a high-emissions climate change scenario. This is equivalent to fewer than five years of current emissions and is consistent with earlier modeling assessments. This estimate is based on the modeled representation of carbon and iron cycling and a highly efficient OIF strategy that may be difficult to achieve in practice. Enhanced surface uptake of major nutrients due to OIF also led to a drop in global net primary production, in addition to that due to climate change alone. By then coupling a complex model of upper trophic levels, the projected declines in animal biomass due to climate change were amplified by around a third due to OIF, with the most negative impacts projected to occur in the low latitude EEZs, which are already facing increasing pressures due to climate change.

This work highlights feedbacks within the ocean’s biogeochemical and ecological systems in response to OIF that emerged over large spatial and temporal scales. Associated pressures on marine ecosystems pose major challenges for proposed management and monitoring. Restricting OIF to the highest latitudes of the Southern Ocean might mitigate some of these negative effects, but this only further reduces the minor mCDR benefit, suggesting that OIF may not make a significant contribution.

Authors
A. Tagliabue (Univ. Liverpool)
B. S. Twining (Bigelow Laboratory)
N. Barrier & O. Maury (MARBEC, IRD, IFREMER, CNRS, Université de Montpellier, France)
M. Berger & Laurent Bopp (ENS-LMD, Paris, France)

IPCC. Summary for Policymakers. in Climate Change, 2022: Mitigation of Climate Change. Contribution of Working Group III to the Sixth Assessment Report of the Intergovernmental Panel on Climate Change (eds. Shukla, P. R. et al.) (Cambridge University Press, 2022).

Introducing the Coastal Ocean Data Analysis Product in North America (CODAP-NA)

Posted by mmaheigan

· Friday, October 22nd, 2021

Coastal ecosystems are hotspots for commercial and recreational fisheries, and aquaculture industries that are susceptible to change or economic loss due to ocean acidification. These coastal ecosystems support about 90% of the global fisheries yield and 80% of the known marine fish species, and sustain ecosystem services worth $27.7 Trillion globally (a number larger than the U.S. economy). Despite the importance of these areas and economies, internally-consistent data products for water column carbonate and nutrient chemistry data in the coastal ocean—vital to understand and predict changes in these systems—currently do not exist. A recent study published in Earth Syst. Sci. Data compiled and quality controlled discrete sampling-based data—inorganic carbon, oxygen, and nutrient chemistry, and hydrographic parameters collected from the entire North American ocean margins—to create a data product called the Coastal Ocean Data Analysis Product for North America (CODAP-NA) to fill the gap. This effort will promote future OA research, modeling, and data synthesis in critically important coastal regions to help advance the OA adaptation, mitigation, and planning efforts by North American coastal communities; and provides a foothold for future synthesis efforts in the coastal environment.

Figure caption. Sampling stations of the CODAP-NA data product.

Authors:
Li-Qing Jiang (University of Maryland; NOAA NCEI)
Richard A. Feely (NOAA PMEL)
Rik Wanninkhof (NOAA AOML)
Dana Greeley (NOAA PMEL)
Leticia Barbero (University of Miami; NOAA AOML)
Simone Alin (NOAA PMEL)
Brendan R. Carter (University of Washington; NOAA PMEL)
Denis Pierrot (NOAA AOML)
Charles Featherstone (NOAA AOML)
James Hooper (University of Miami; NOAA AOML)
Chris Melrose (NOAA NEFSC)
Natalie Monacci (University of Alaska Fairbanks)
Jonathan Sharp (University of Washington; NOAA PMEL)
Shawn Shellito (University of New Hampshire)
Yuan-Yuan Xu (University of Miami; NOAA AOML)
Alex Kozyr (University of Maryland; NOAA NCEI)
Robert H. Byrne (University of South Florida)
Wei-Jun Cai (University of Delaware)
Jessica Cross (NOAA PMEL)
Gregory C. Johnson (NOAA PMEL)
Burke Hales (Oregon State University)
Chris Langdon (University of Miami)
Jeremy Mathis (Georgetown University)
Joe Salisbury (University of New Hampshire)
David W. Townsend (University of Maine)

Chesapeake Bay acidification partially offset by submerged aquatic vegetation

Posted by mmaheigan

· Wednesday, September 30th, 2020

Ocean acidification is often enhanced by eutrophication and subsequent hypoxia and anoxia in coastal waters, which collectively threaten marine organisms and ecosystems. Acidification is particularly of concern for organisms that form shells and skeletons from calcium carbonate (CaCO₃) such as commercially important shellfish species. Given that CaCO₃ mineral dissolution can increase the total alkalinity of water and neutralize anthropogenic and metabolic CO₂, it is important to include CaCO₃ cycle in the coastal water acidification study. However, very few studies have linked CaCO₃ dissolution to the timing and location of its formation in coastal waters. A recent study from the Chesapeake Bay published in Nature Geoscience reveals the occurrence of a bay-wide pH-buffering mechanism resulting from spatially decoupled CaCO₃ mineral cycling (Figure 1). Photosynthesis by submerged aquatic vegetation at the head of the Bay and in other shallow, nearshore waters can remove nutrient pollution from the Bay, generate very high pH, and elevate the carbonate mineral saturation state (Figure 1). This facilitates the formation of CaCO₃ minerals, which are then transported downstream along with other biologically produced carbonate shells into acidic subsurface waters, where they dissolve. This dissolution of carbonate minerals helps “buffer” the water against pH decreases and even drive pH increases. This finding has great ecological and natural resource management significance, in that coastal nutrient management and reduction via the resurgence of submerged aquatic vegetation can help mitigate low oxygen and acidification stress for these environments and organisms.

Figure 1: Conceptual model of the self-regulated pH-buffering mechanism in the Chesapeake Bay. Calcium carbonate is formed within the high-pH submerged aquatic vegetation beds in shallow waters (top left and upper part of diagram, all Shoals with SAV), where it could be subsequently transported longitudinally and/or laterally into the deep main channel of the mid and lower bay (center) and upon dissolution, increase pH buffering capacity and alleviate coastal acidification (lower section).

Authors:
Jianzhong Su (University of Delaware, Xiamen University)
Wei-Jun Cai (University of Delaware)
Jean Brodeur (University of Delaware)
Baoshan Chen (University of Delaware)
Najid Hussain (University of Delaware)
Yichen Yao (University of Delaware)
Chaoying Ni (University of Delaware)
Jeremy Testa (University of Maryland Center for Environmental Science)
Ming Li (University of Maryland Center for Environmental Science)
Xiaohui Xie (University of Maryland Center for Environmental Science, Second Institute of Oceanography)
Wenfei Ni (University of Maryland Center for Environmental Science)
K. Michael Scaboo (University of Delaware)
Yuanyuan Xu (University of Delaware)
Jeffrey Cornwell (University of Maryland Center for Environmental Science)
Cassie Gurbisz (St. Mary’s College of Maryland)
Michael S. Owens (University of Maryland Center for Environmental Science)
George G. Waldbusser (Oregon State University)
Minhan Dai (Xiamen University)
W. Michael Kemp (University of Maryland Center for Environmental Science)

The role of nutrient trapping in promoting shelf hypoxia in the southern Benguela upwelling system

Posted by mmaheigan

· Thursday, September 3rd, 2020

The southern Benguela upwelling system (SBUS) off southwest Africa is an exceptionally fertile ocean region that supports valuable commercial fisheries. The productivity of this system derives from the upwelling of nutrient-rich Subantarctic Mode Water, and from the concurrent entrainment of nutrients regenerated proximately on the expansive continental shelf. The SBUS is prone to severe seasonal hypoxic events that decimate regional fisheries, occurrences of which are inextricably linked to the inherent nutrient dynamics. In a study recently published in JGR Oceans, the authors sought to understand the mechanisms sustaining elevated concentrations and seasonally-variable distributions of nutrients in the SBUS, in relation to the subsurface oxygen content. Inter-seasonal measurements of nutrients and nitrate isotope ratios across the SBUS in 2017 revealed that upwards of 48% (summer) and 63% (winter) of the on‐shelf nutrients derived from regeneration in situ. The severity of hypoxia at the shelf bottom, in turn, correlated with the incidence of regenerated nutrients. The accrual of nutrients at the shelf bottom appears to be aided by hydrographic fronts that restrict offshore transport, trapping regenerated nutrients on the SBUS shelf and increasing the pool of nutrients available for upwelling – ultimately contributing to hypoxic events. This study underscores the need – if we are to develop a mechanistic and predictive understanding of hypoxia in the SBUS and elsewhere – to elucidate the role of shelf circulation in promoting the accrual of regenerated nutrients on the continental shelf. The next step is to combine new and existing observations with quantitative simulations to further interrogate the coupled physical-biogeochemical mechanisms that modulate the intensity of hypoxia.

Figure caption: Schematic of proposed nutrient-trapping mechanism: Deep nutrient-rich Subantarctic Mode Water (SAMW) acquires more nutrients as it passes over the shelf sediments from the regeneration of exported particulate organic material (POM). The production of this POM is fueled by nutrients stripped from the surface waters advecting back off-shore. The thickness of the arrows represents nutrient concentrations. Triangles indicate the positions of the Shelf Break Front (SBF) and Columbine Front (CF), coincident with an observed subduction of the Ekman layer and downwelling at the inner front boundary.

Authors
Raquel Flynn (University of Cape Town)
Julie Granger (University of Connecticut)
Jennifer Veitch (South African Environmental Observation Network)
Samantha Siedlecki (University of Connecticut)
Jessica Burger (University of Cape Town)
Keshnee Pillay (South Africa Department of Environment, Forestry and Fisheries)
Sarah Fawcett (University of Cape Town)

Predicting marine ecosystem futures

Posted by mmaheigan

· Wednesday, September 4th, 2019

Earth System Models (ESMs) are powerful and effective tools for exploring and predicting marine ecosystem response to environmental change, including biogeochemical processes that underlie threats to ocean health such as ocean acidification, deoxygenation, and changes in productivity. Seasonal to interannual marine biogeochemical predictions with ESMs hold great promise for exploring links between climate and marine resources such as fisheries but have thus far been challenged by limitations associated with observational initialization, model structure, and computational availability. In a recent study published in Science, authors integrated the Geophysical Fluid Dynamics Laboratory’s (GFDL) COBALT (Carbon, Ocean Biogeochemistry and Lower Trophics) marine biogeochemical model with seasonal to multi-annual climate predictions from GFDL’s CM2.1 climate model to examine marine ecosystem futures on these shorter time scales. The global biogeochemical forecasts were initialized on the first of each month between 1991 and 2017 with 12 ensemble members in each prediction, creating a database of nearly 4000 forecasts and 8000 simulation years. The model skillfully predicted seasonal to multi-annual chlorophyll fluctuations in many ocean regions (Figure 1).

Figure 1: Prediction skill in reproducing observed variations of monthly chlorophyll anomaly. (Top) Correlation coefficient between predicted and observed chlorophyll at 1-3 month lead time during the period 1997-2017. Stippled areas indicate that the correlation is significantly greater than 0 with 95% confidence. Areas with less than 80% satellite chlorophyll coverage are masked in grey. (Lower panels) Correlation coefficient between predicted and observed chlorophyll as a function of forecast initialization month (x-axis) and lead time (y-axis) in tropical Pacific, Indian, North Atlantic, North Pacific, and South Pacific oceans. In all panels, the darker the red, the higher the correlation up to a perfect correlation of 1.0. White indicates no correlation, while blue indicates negative correlation.

These results suggest that annual fish catches in selected large marine ecosystems can be predicted from chlorophyll and sea surface temperature anomalies up to 2-3 years in advance. Given that fisheries predictions sometimes failed to the point of commercial stock collapse in the past, this prediction capacity could be vital for fisheries managers. Biogeochemical prediction systems can extend beyond sea surface temperature and chlorophyll to include other potential drivers (e.g., oxygen, acidity, net primary production, zooplankton, etc.) as highly valuable tools for marine resource managers of dynamic and changing ecosystems.

Authors:
Jong-Yeon Park (Princeton Univ, NOAA GDFL, Chonbuk National Univ., Korea)
Charles A. Stock, John P. Dunne, Xiaosong Yang, and Anthony Rosati (NOAA GFDL)

You better repeat it: Serial ocean acidification experiments on fish early life stages

Posted by mmaheigan

· Tuesday, March 5th, 2019

To detect potential effects of acidification on marine organisms, experimenters most commonly use within-experiment replication, but repeating the experiments themselves is rarely done. While the first approach suffices to detect major CO₂ effects, other potentially important responses may get detected and robustly quantified only via serial experimentation. A study by Baumann et al. in Biology Letters comprises a meta-analysis of 20 standard CO₂ exposure experiments conducted over six years on Atlantic silverside (Menidia menidia) offspring.

Figure 1: Robust estimate of silverside CO₂ sensitivity based on serial experimentation. (A, B) Mean CO₂ effect size calculated as the log-transformed response ratio of six early life history traits measured at 20 standard experiments between 2012-2017 (Error: bootstrapped 95% confidence intervals). (C) Seasonal change in CO₂ sensitivity in silverside early life stages. Each symbol represents an individual experiment, using offspring obtained by fertilizing wild spawners throughout their spring/summer spawning season.

Silversides are an abundant and ecologically important forage fish in the North Atlantic. The study revealed that during early life stages, Atlantic silversides tolerate pCO₂levels up to ~2,000 µatm, with seasonal shifts in sensitivity. However, this early exposure to high pCO₂ levels reduces embryo survival by 9% and overall survival by 13% (Figure 1). Future ocean acidification could cause reduced survival of these and other forage fish, and thus impact their diverse marine predators, including seabirds and commercially important fish species. This sustained experimental work resulted in the most robustly constrained estimates of average CO₂ effect sizes for a marine organism to date, demonstrating the utility of serial experimentation as a powerful tool for assessing organism responses to changing CO₂.

Authors:
Hannes Baumann
Emma L. Cross
Chris S. Murray
(all University of Connecticut)

When marine-terminating glaciers ‘pump’ the ocean

Posted by mmaheigan

· Wednesday, October 10th, 2018

How will increasing meltwater from Greenland affect the biogeochemistry of the ocean? Release of meltwater into the ocean has physical and biogeochemical effects on the local water column. With respect to nutrient availability, meltwater supplies the bioessential nutrients iron and silicic acid but is deficient in nitrate and phosphate. However, despite very low meltwater nitrate and phosphate concentrations, pronounced summertime phytoplankton blooms are observed in many, though not all, of Greenland’s large fjord systems. These unusual summertime blooms are associated with meltwater from marine-terminating glaciers. So if the meltwater itself is not supplying nitrate and phosphate that these blooms require, what is the source of the nutrients that support these blooms?

An illustration of how changing the depth of a glacier affects downstream productivity

A recent study published in Nature Communications shows that when meltwater is released below sea level under large marine-terminating glaciers, it rises rapidly towards the surface in buoyant discharge plumes. As these plumes rise, they entrain large quantities of deep, nutrient-rich seawater. This vertical transport, or ‘pumping’, of these nutrients to the surface sustains unusually high summertime productivity in Greenland’s fjords. Conversely, when meltwater is released at the ocean surface, primary production is reduced because the meltwater itself lacks the nitrate and phosphate required to fuel phytoplankton blooms. Consequently, the inland retreat of Greenland’s large marine-terminating glaciers is ultimately bad news for summertime marine phytoplankton communities. As the depth of the marine-terminating glaciers shoals, their associated nutrient ‘pumps’ collapse, which will likely have negative effects on primary production and associated inshore fisheries.

Authors:
M.J. Hopwood (GEOMAR)
D. Carroll (Jet Propulsion Laboratory)
T.J. Browning (GEOMAR)
L. Meire (Royal Netherlands Institute for Sea Research and Greenland Climate Research Centre)
J. Mortensen (Greenland Climate Research Centre)
S. Krisch (GEOMAR)
E.P. Achterberg (GEOMAR)

Untangling the mystery of domoic acid events: A climate-scale perspective

Posted by mmaheigan

· Thursday, August 3rd, 2017

The diatom Pseudo-nitzchia produces a neurotoxin called domoic acid, which in high concentrations affects wildlife ranging from mussels and crabs to seabirds and sea lions, as well as humans. In humans, the effects of domoic acid poisoning can range from gastrointestinal distress to memory loss, and even death. Despite being studied in laboratories since the late 1980s, there is no consensus on the environmental conditions that lead to domoic acid events. These events are most frequent and impactful in eastern boundary current regions such as the California Current System, which is bordered by Washington, Oregon, and California. In Oregon alone, there have been six major domoic acid events: 1996, 1998-1999, 2001, 2002-2006, 2010, 2014-2015. McKibben et al. (2017) investigated the regulation of domoic acid at a climate scale to develop and test an applied risk model for the US West Coast” to read “McKibben et al. (2017) investigated the regulation of domoic acid at regional and decadal scales in order to develop and test an applied risk model for the impact of climate on the US West Coast. They used the PDO and ONI climate variability indices, averages of monthly and 3 month running means of SST anomaly values and variability to look at basin-scale ocean conditions. At a local scale, data were from zooplankton sampling every two to four weeks between 1996 to 2015 at hydrographic station offshore of Newport, OR. Additionally, the NOAA NCDC product “Daily Optimum Interpolation, Advanced Very High Resolution Radiometer Only, Version 2, Final+Preliminary SST” was used to obtain the monthly SST anomaly metric, based on combined in situ and satellite data.

(A) Warm and cool ocean regimes, (B) local SST anomaly, and (C and D) biological response. (A) PDO (red or blue vertical bars) and ONI (black line) indices; strong (S) to moderate (M) El Nino (+1) and La Nina (−1) events are labeled. (B) SST anomaly 20 nm off central OR. (C) The CSR anomaly 5 nm off central OR. (D) Monthly OR coastal maximum DA levels in razor clams (vertical bars); horizontal black line is the 20-ppm closure threshold. Black line in D shows the spring biological transition date (right y axis). At the top of the figure, black boxes indicate the duration of upwelling season each year; red vertical bars indicate the timing of annual DA maxima in relationship to upwelling. Gray shaded regions are warm regimes based on the PDO. Dashed vertical lines indicate onset of the six major DA events. The September 2014 arrival of the NE Pacific Warm Anomaly (colloquially termed “The Blob”) to the OR coastal region is labeled on B. “X” symbols along the x axes indicate that no data were available for that month (B–D).

Their findings show that these events have occurred when there is advection of warmer water masses onto the continental shelf from southern or offshore areas. When the warm phase of the Pacific Decadal Oscillation (PDO) and El Niño coincide, the effect is additive. In the warm regime years, there is a later spring biological transition date, weaker alongshore currents, elevated water temperatures, and plankton communities are dominated by subtropical rather than subarctic species. The authors also note relative differences between the prevalence and phenology of domoic acid events in OR, CA and WA, which warrants further study via regional-scale modeling. Overall, this research shows a clear and enhanced risk of toxicity in shellfish during warm phases of natural climate oscillations. If predictions of more extreme warming come to bear, this would potentially lead to increased DA event intensity and frequency in coastal zones around the globe. This will not only affect wildlife, but may cause significant closures of economically important fisheries (e.g., Dungeness crab, anchovy, mussel, and razor clam), which would impact local communities and native populations.

Authors:
Morgaine McKibben (Oregon State Univ., NOAA Northwest Fisheries Science Center)
William Peterson (NOAA Northwest Fisheries Science Center)
Michelle Wood (Univ. Oregon)
Vera L. Trainer (NOAA Northwest Fisheries Science Center)
Matthew Hunter (Oregon Dept. Fish & Wildlife)
Angelicque E. White (Oregon State Univ.)

Reconciling fisheries catch and ocean productivity in a changing climate

Posted by mmaheigan

· Thursday, March 16th, 2017

Phytoplankton provide the energy that fuels marine food webs, yet differences in fisheries catch across global ecosystems far exceed accompanying differences in phytoplankton production. Nearly 50 years ago, John Ryther hypothesized that this contrast must arise from synergistic interactions between phytoplankton production and food webs. New perspectives on global fish catch, fishing effort, and a prototype high-resolution global earth system model allowed us to revisit Ryther’s supposition and explore its implications under climate change. After accounting for a small number of lightly fished ecosystems, we find that stark differences in regional catch can be explained with an energetically constrained model that a) resolves large inter-regional differences in the benthic and pelagic energy pathways connecting phytoplankton and fish; b) reduces trophic transfer efficiencies in warm, tropical ecosystems; and, less critically, c) associates elevated trophic transfer efficiencies with benthic systems. The same food web processes that accentuate spatial differences in phytoplankton production in the contemporary ocean also accentuated temporal trends under climate change, with projected fish catch changes in some areas exceeding 50% (Figure 1). Our results, recently published in PNAS, demonstrate the importance of marine resource management strategies that are robust to potentially significant changes in fisheries productivity baselines. These results also provide impetus for efforts to improve constraints on regional ocean productivity projections that often disagree in present earth system models.

Figure 1: Projected percent changes in net phytoplankton production (left) and fisheries catch (right) between 2050-2100 and 1950-2000 under a high greenhouse gas emission scenario (RCP8.5) in GFDL’s ESM2M-COBALT Earth System Model. Contours are shown for +/- 50%.

Authors: Charles A. Stock^a, Jasmin G. John^a, Ryan R. Rykaczewski^b,c, Rebecca G. Asch^d, William W.L. Cheung^e, John P. Dunne^a, Kevin D. Friedland^f, Vicky W.Y. Lam^e, Jorge L. Sarmiento^d, and Reg A. Watson^g

^aGeophysical Fluid Dynamics Laboratory, National Oceanic and Atmospheric Administration
^bSchool of the Earth, Ocean, and Environment, University of South Carolina
^cDepartment of Biological Sciences, University of South Carolina
^dAtmospheric and Oceanic Sciences Program, Princeton University
^eNippon Foundation-Nereus Program, Institute of Oceans and Fisheries, The University of British Columbia
^fNational Marine Fisheries Service, Narragansett, RI
^gInstitute for Marine and Antarctic Studies, University of Tasmania, Australia

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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