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Drivers of recent Chesapeake Bay warming

Posted by mmaheigan

· Friday, August 26th, 2022

Coastal water temperatures have been increasing globally with more frequent marine heat waves threatening marine life and nearshore communities reliant upon these ecosystems. Often, this warming is assumed to be uniform in space and time; however, this is not the case in the Chesapeake Bay, where warming waters play a major role in exacerbating low oxygen levels and indirectly limiting the efficacy of nutrient reduction efforts on land.

New research published in the Journal of the American Water Resources Association combined long-term observations and a hydrodynamic model to quantify the temporal and spatial variability in warming Chesapeake Bay waters, and identify the contributions of different mechanisms driving these historical temperature changes. While winter temperatures have warmed by less than a half a degree over the past 30 years, summer temperatures have warmed by nearly 1.5 °C, with similar increases at the surface and bottom. In cooler months, the atmosphere was the dominant driver of warming throughout the majority of the Bay, but oceanic warming explained more than half of the increased summer temperatures in the southern Bay nearest the Atlantic.

Figure 1: Relative contribution of different factors to warm-month Chesapeake Bay temperature change over the period 1985-2015. Percentages correspond to average main channel contributions for each component.

Warming temperatures have potentially significant implications for the future size of the Chesapeake Bay dead zone, and the marine species directly affected by these low oxygen conditions. Better quantifying warming contributions from the atmosphere, ocean, sea level, and rivers will also help constrain regional temperature projections throughout the estuary. More accurate projections of future Bay temperatures can help coastal managers better understand the potential for invasive species expansion and endemic species loss, impacts to fisheries and aquaculture, and how changes to ecosystem processes may impact coastal communities dependent on a healthy Bay.

Authors:
Kyle E. Hinson (Virginia Institute of Marine Science, William & Mary)
Marjorie A. M. Friedrichs (Virginia Institute of Marine Science, William & Mary)
Pierre St-Laurent (Virginia Institute of Marine Science, William & Mary)
Fei Da (Virginia Institute of Marine Science, William & Mary)
Raymond G. Najjar (The Pennsylvania State University)

Why are sand lance embryos so sensitive to future high CO2-oceans?

Posted by mmaheigan

· Friday, August 26th, 2022

Two decades of ocean acidification experiments have shown that elevated CO₂ can affect many traits in fish early life stages. Only few species, however, show direct CO₂-induced survival reductions. This may partly reflect a bias in our current empirical record, which is dominated by species from nearshore tropical-to-temperate environments. There, these organisms already experience highly variable CO₂ conditions. In contrast, fishes from more offshore habitats, especially at higher latitudes are adapted to more CO₂-stable conditions, which could make them more CO₂-sensitive. This group of fishes is still underrepresented in the literature, despite its enormous commercial and ecological importance.

To help address this gap, we conducted new experimental work on northern sand lance Ammodytes dubius, a key forage fish on offshore Northwest Atlantic sand banks with trophic links to more than 70 different predator species of fish, squid, seabirds, and marine mammals. On Stellwagen Bank in the southern Gulf of Maine, sand lance are the ‘backbone’ of the eponymous National Marine Sanctuary.

We followed up on the intriguing findings of a pilot study a few years ago. Over two years and two trials, we again produced embryos from wild, Stellwagen Bank spawners and reared them at several pCO₂ levels (~400−2000 μatm) in combination with static and dynamic temperatures. Again, we observed consistently large CO₂-induced reductions in hatching success (-23% at 1,000 µatm, -61% at ~2,000 µatm), but this time the effects were temperature-independent.

Intriguingly, we again saw that many sand lance embryos at high CO₂ treatments did not merely arrest in their development (indicative of acidosis), but appeared to develop fully to hatch but were somehow incapable of doing so. We show several lines of evidence supporting the hypothesis that CO₂ directly impairs hatching in this species. Most fish rely on hatching enzymes that help embryos break the chorion (egg shell), but these ubiquitous enzymes may work less efficiently under high CO₂, low pH conditions.

For additional context, we also derived long-term, seasonal pCO₂ projections specifically for Stellwagen Bank, which together with the experimental data suggested that increasing CO₂ levels alone could reduce sand lance hatching success to 71% of contemporary levels by the year 2100.

We believe that the importance of sand lances as forage fishes across most northern hemisphere shelf ecosystem warrants a strategic effort of OA researchers to begin testing other sand lance species or populations to understand the magnitude of the problem and its underlying mechanisms.

Authors:
Hannes Baumann (University of Connecticut)
Lucas Jones (University of Connecticut)
Christopher Murray (University of Washington)
Samantha Siedlecki (University of Connecticut)
Michael Alexander (NOAA Physical Sciences Laboratory)
Emma Cross (Southern Connecticut State University)

How does the competition between phytoplankton and bacteria for iron alter ocean biogeochemical cycles?

Posted by mmaheigan

· Friday, August 26th, 2022

Free-living bacteria play a key role in cycling essential biogeochemical resources in the ocean, including iron, via their uptake, transformation, and release of organic matter throughout the water column. Bacteria process half of the ocean’s primary production, remineralize dissolved organic matter, and re-direct otherwise lost organic matter to higher trophic levels. For these reasons, it is crucial to understand what factors limit the growth of bacteria and how bacteria activities impact global ocean biogeochemical cycles.

In a recent study, Pham and colleagues used a global ocean ecosystem model to dive into how iron limits the growth of free-living marine bacteria, how bacteria modulate ocean iron cycling, and the consequences to marine ecosystems of the competition between bacteria and phytoplankton for iron.

Figure 1: (a) Iron limitation status of bacteria in December, January, and February (DJF) in the surface ocean. Low values (in blue color = close to zero) mean that iron is the limiting factor for the growth of bacteria; (b) Bacterial iron consumption in the upper 120m of the ocean and (c) Changes (anomalies) in export carbon production when bacteria have a high requirement for iron.

Through a series of computer simulations performed in the global ocean ecosystem model, the authors found that iron is a limiting factor for bacterial growth in iron-limited regions in the Southern Ocean, the tropical, and the subarctic Pacific due to the high iron requirement and iron uptake capability of bacteria. Bacteria act as an iron sink in the upper ocean due to their significant iron consumption, a rate comparable to phytoplankton. The competition between bacteria and phytoplankton for iron alters phytoplankton bloom dynamics, ocean carbon export, and the availability of dissolved organic carbon needed for bacterial growth. These results suggest that earth system models that omit bacteria ignore an important organism modulating biogeochemical responses of the ocean to future changes.

Authors:
Anh Le-Duy Pham (Laboratoire d’Océanographie et de Climatologie: Expérimentation et Approches Numériques (LOCEAN), IPSL, CNRS/UPMC/IRD/MNHN, Paris, France)
Olivier Aumont (Laboratoire d’Océanographie et de Climatologie: Expérimentation et Approches Numériques (LOCEAN), IPSL, CNRS/UPMC/IRD/MNHN, Paris, France)
Lavenia Ratnarajah (University of Liverpool, United Kingdom)
Alessandro Tagliabue (University of Liverpool, United Kingdom)

What can algae tell us about translating laboratory science to nature?

Posted by mmaheigan

· Thursday, June 9th, 2022

Ocean acidification research has grown over the past few decades. Much of recent research documents negative impacts of changing carbonate chemistry on calcifying marine organisms in laboratory experiments. At the 2018 Ocean Acidification PI Meeting, a group of us asked “Can these laboratory responses to ocean acidification be scaled up to accurately predict the responses of marine ecosystems?” To answer this research question, we developed a semi-quantitative synthesis of benthic calcifying algae responses to ocean acidification, recently published in the ICES Journal of Marine Science.

Figure 1. Comparing directional responses of individuals and communities to acidification in laboratory and field settings highlights mismatches. Specifically, field studies document higher proportion of negative responses compared to laboratory experiments. We provide a series of recommendations for future research to better bridge this gap of understanding in responses to ocean acidification. Figure modified from Page et al. 2022.

We detail in the paper how the proportion of positive, neutral, and negative responses in laboratory experiments often didn’t match field observations. Additionally, laboratory experiments mainly report short-term responses (days to weeks) across tropical and temperate locations. In contrast, field studies emphasize long-term responses (months to years) from fewer global locations. Using our synthesis, we developed nine recommendations that will enhance our ability to translate laboratory experiment results into actual responses of marine taxa to ongoing and future acidification in the natural environment. These future research directions are applicable not only to ocean acidification studies but can be directly applied to the broader field of climate change. We hope these recommendations will lead to greater confidence in our projections of climate change impacts at different ecological scales, and better inform the conservation and management of our valuable marine ecosystems.

Backstory

Initially, we set out to answer this research question through a meta-analysis comparing the effect size of the impacts of ocean acidification on benthic calcifying macroalgae in laboratory and field settings. We quickly realized this approach was not going to work because of the much smaller number of responses recorded in field settings, the different methods used, and response parameters measured between the laboratory and field; these differences made calculating and comparing effect sizes impossible. Therefore, we landed on the approach of conducting a semi-quantitative synthesis to compare directional responses in laboratory and field settings. The results of this synthesis and the process of developing a robust research approach to answer our question inspired us to discuss and develop the recommendations for future research presented in the paper.

Authors (affils and Twitter handles)
Heather N. Page (Sea Education Association) @heathernicopage
Keisha D. Bahr (Texas A&M University – Corpus Christi) @thebahrlab
Tyler Cyronak (Nova Southeastern University) @tcyronak
Elizabeth B. Jewett (National Oceanic and Atmospheric Administration) @LibbyJewett
Maggie D. Johnson (King Abdullah University of Science and Technology) @MaggieDJohnson
Sophie J. McCoy (University of North Carolina at Chapel Hill) @MarEcology

Zooplankton evolutionary rescue is limited by warming and acidification interactions

Posted by mmaheigan

· Friday, November 19th, 2021

A key issue facing ocean global change scientists is predicting the fate of biota under the combined effects of ocean warming and acidification (OWA). In addition to the constraints of studying multifactor drivers, predictions are hampered by few evolutionary studies, especially for animal populations. Evolutionary studies are essential to assess the possibility of evolutionary rescue under OWA– the recovery of fitness that prevents population extirpation in the face of environmental change.

Figure 1. Population fitness of the copepod Acartia tonsa vs generation under ambient, AM (18^oC, 400 µat pCO₂), ocean warming, OW (22^oC, 400 µat pCO₂), ocean acidification, ocean acidification (18^oC, 2000 µat pCO₂), and ocean warming and acidification ( 22^oC, 2000 µat pCO₂). Shown are means and 95% confidence intervals around the mean. The purple line shows that while fitness decreased after the 12^th generation, it was still considerably higher than at generation zero. Treatment lines are offset for clarity. N_o and N_τ (Y-axis legend) represent population size at the beginning and end of a generation (τ), and their ratio is the population fitness. Adapted from Dam et al. (2021).

A paper by Dam et al. published in Nature Climate Change examined the response of a ubiquitous copepod (zooplankter) to OWA for 25 generations to test for evolutionary rescue (Fig. 1). Using a suite of life-history traits, the researchers determined population fitness (the net reproductive rate per generation) under ambient, ocean warming, ocean acidification and OWA conditions. While population fitness decreased drastically under OWA conditions, it recovered in a few generations. However, after 12 generations under OWA, in contrast to OW or OA, fitness started to decrease again, suggesting incomplete evolutionary rescue driven by antagonistic interactions between warming and acidification. Such interactions add complexity to predictions of the fate of the oceanic biota under climate change.

Limited copepod evolutionary rescue would mean lower fisheries yields under OWA conditions as copepods are a main food source for forage fish. Copepods are also important vectors of the sequestration of CO₂ to deeper waters of the ocean. Limited copepod adaptation under OWA could weaken the efficiency of the biological carbon pump.

Authors:
Hans G. Dam (University of Connecticut)
James de Mayo (University of Connecticut)
Gihong Park (University of Connecticut)
Lydia Norton (University of Connecticut)
Xuejia He (Jinan University, China)
Michael B. Finiguerra (University of Connecticut)
Hannes Baumann (University of Connecticut)
Reid S. Brennn (University of Vermont)
Melissa H. Pespeni (University of Vermont)

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)

The ephemeral and elusive COVID blip in ocean carbon

Posted by mmaheigan

· Monday, September 20th, 2021

The global pandemic of the last nearly two years has affected all of us on a daily and long-term basis. Our planet is not exempt from these impacts. Can we see a signal of COVID-related CO₂ emissions reductions in the ocean? In a recent study, Lovenduski et al. apply detection and attribution analysis to output from an ensemble of COVID-like simulations of an Earth system model to answer this question. While it is nearly impossible to detect a COVID-related change in ocean pH, the model produces a unique fingerprint in air-sea DpCO₂ that is attributable to COVID. Challengingly, the large interannual variability in the climate system makes this fingerprint difficult to detect at open ocean buoy sites.

This study highlights the challenges associated with detecting statistically meaningful changes in ocean carbon and acidity following CO₂ emissions reductions, and reminds the reader that it may be difficult to observe intentional emissions reductions — such as those that we may enact to meet the Paris Climate Agreement – in the ocean carbon system.

Figure caption: The fingerprint (pink line) of COVID-related CO2 emissions reductions in global-mean surface ocean pH and air-sea DpCO2, as estimated by an ensemble of COVID-like simulations in an Earth system model. While the pH fingerprint is not particularly exciting, the air-sea DpCO2 fingerprint displays a temporary weakening of the ocean carbon sink in 2021 due to COVID emissions reductions.

Authors:
Nikki Lovenduski (University of Colorado Boulder)
Neil Swart (Canadian Centre for Climate Modeling and Analysis)
Adrienne Sutton (NOAA Pacific Marine Environmental Laboratory)
John Fyfe (Canadian Centre for Climate Modeling and Analysis)
Galen McKinley (Columbia University and Lamont Doherty Earth Observatory)
Chris Sabine (University of Hawai’i at Manoa)
Nancy Williams (University of South Florida)

Sea ice loss amplifies CO2 increase in the Arctic

Posted by mmaheigan

· Thursday, January 7th, 2021

Warming and sea ice loss over the past few decades have caused major changes in sea surface partial pressure of CO₂ (pCO₂) of the western Arctic Ocean, but detailed temporal variations and trends during this period of rapid climate-driven changes are not well known.

Based on an analysis of an international Arctic pCO₂ synthesis data set collected between 1994-2017, the authors of a recent paper published in Nature Climate Change observed that summer sea surface pCO₂ in the Canada Basin is increasing at twice the rate of atmospheric CO₂ rise. Warming, ice loss and subsequent CO₂ uptake in the Basin are amplifying seasonal pCO₂ changes, resulting in a rapid long-term increase. Consequently, the summer air-sea CO₂ gradient has decreased sharply and may approach zero by the 2030s, which is reducing the basin’s capacity to remove CO₂from the atmosphere. In stark contrast, sea surface pCO₂ on the Chukchi Shelf remains low and relatively constant during this time frame, which the authors attribute to increasingly strong biological production in response to higher intrusion of nutrient-rich Pacific Ocean water onto the shelf as a result of increased Bering Strait throughflow. These trends suggest that, unlike the Canada Basin, the Chukchi Shelf will become a larger carbon sink in the future, with implications for the deep ocean carbon cycle and ecosystem.

As Arctic sea ice melting accelerates, more fresh, low-buffer capacity, high-CO₂ water will enter the upper layer of the Canada Basin, which may rapidly acidify the surface water, endanger marine calcifying organisms, and disrupt ecosystem function.

Figure. 1: TOP) Sea surface pCO₂ trend in the Canada Basin and Chukchi Shelf. The grey dots represent the raw observations of pCO₂, black dots are the monthly mean of pCO₂ at in situ SST, and red dots are the monthly means of pCO₂ normalized to the long-term means of SST. The arrows indicate the statistically significant change in ∆pCO₂. BOTTOM) Sea ice-loss amplifying surface water pCO₂ in the Canada Basin. Black dots represent the initial condition for pCO₂ and DIC at -1.6 ℃. The arrows indicate the processes of warming (red), CO₂ uptake from the atmosphere (green), dilution by ice meltwater (blue). The yellow shaded areas indicate the possible seasonal variations of pCO₂, which are amplified by the synergistic effect of ice melt, warming and CO₂ uptake.

Authors:
Zhangxian Ouyang (University of Delaware, USA),
Di Qi (Third Institute of Oceanography, China),
Liqi Chen (Third Institute of Oceanography, China),
Taro Takahashi† (Columbia University, USA),
Wenli Zhong (Ocean University of China, China),
Michael D. DeGrandpre (University of Montana, USA),
Baoshan Chen (University of Delaware, USA),
Zhongyong Gao (Third Institute of Oceanography, China),
Shigeto Nishino (Japan Agency for Marine-Earth Science and Technology, Japan),
Akihiko Murata (Japan Agency for Marine-Earth Science and Technology, Japan),
Heng Sun (Third Institute of Oceanography, China),
Lisa L. Robbins (University of South Florida, USA),
Meibing Jin (International Arctic Research Center, USA),
Wei-Jun Cai* (University of Delaware, USA)

Warming counteracts acidification in temperate crustose coralline algae communities

Posted by mmaheigan

· Friday, November 6th, 2020

Seawater carbonate chemistry has been altered by dramatic increases in anthropogenic CO₂ release and global temperatures, leading to significant changes in rocky shore habitats and the metabolism of most marine organisms. There has been recent interest in how these anthropogenic stresses affect crustose coralline algae (CCA) communities because CCA photosynthesis and calcification are directly influenced by seawater carbonate chemistry. CCA is a foundation species in temperate macroalgal communities, where species succession and rocky shore community structure are particularly susceptible to anthropogenic disturbance. In particular, the disappearance of turf and foliose macroalgae caused by climate change and herbivore pressure results in the dominance of CCA (Figure 1a).

Figure 1: (a) Examples of crustose coralline algae (CCA)-dominated seaweed bed in the East Sea of Korea showing barren ground dominated by CCA (bright white and pink color on the rock; see arrows) on a rocky subtidal zone grazed by sea urchins. (b) Specific growth rate of marginal encrusting area under future climate conditions.

In a recent study published in Marine Pollution Bulletin, the authors conducted a mesocosm experiment to investigate the sensitivity of temperate CCA Chamberlainium sp. to future climate stressors, as simulated by three experimental treatments: 1) Acidification: doubled CO₂; 2) Warming: +5ºC; and 3) Greenhouse: doubled CO₂ and +5ºC. After a 47-day acclimation period, when compared with present-day (control: 490 μatm and 20ºC) conditions, the Acidification treatment showed decreased photosynthesis rates of Chamberlainium sp, whereas the Warming treatment showed increased photosynthesis. The Acidification treatment also showed reduced encrusting growth rates relative to the Control, but when acidification was combined with warming in the Greenhouse treatment, encrusting growth rates increased substantially (Figure 1b). Taken together, these results suggest that the negative ecophysiological responses of Chamberlainium sp to acidification are ameliorated by elevated temperatures in a greenhouse world. In other words, if the foliose macroalgal community responses negatively in the greenhouse environment, the dominance of CCA will increase further, and the biodiversity of the algae community will be reduced.

Authors:
Ju-Hyoung Kim (Faculty of Marine Applied Biosciences, Kunsan National University)
Il-Nam Kim (Department of Marine Science, Incheon National University)

Timing matters: Correcting float-based measurements of diurnal oxygen variability

Posted by mmaheigan

· Friday, November 6th, 2020

Despite its fundamental importance to the global carbon cycle, climate, and marine ecosystems, oceanic primary production is grossly under-sampled. Autonomous platforms represent an important frontier for expanding measurements of marine primary productivity in time and space, but this requires the establishment of robust, standardized methods to obtain reliable data from these platforms. Using data from profiling floats deployed in the northern Gulf of Mexico, authors of a recent study published in Biogeosciences demonstrated, for the first time, that daily cycles of dissolved oxygen can be observed with Argo-type profiling floats. The floats were instructed to profile continuously, resulting in about one profile every three hours. The floats recorded data both on the ascent (upcast) and the descent (downcast). Adjacent casts showed hysteresis in gradient areas, i.e. a lag in the concentration measurement, due to the slow response time of oxygen sensors.

Figure 1: Example of raw oxygen measurements from a downcast (dark purple line) and an upcast (dark green line) and corrected profiles (lighter purple and green lines) in (a) density and (b) pressure coordinates. (c) Upcasts and downcasts (top 150 m) plotted against each other with raw data (purple) and data corrected according to the new method (red). (d) The root-mean-square difference (RMSD) between the upcast and downcast after correcting casts for a range of time constants (τ), showing an optimal τ value in this case of 76 s (red dot).

To correct for these measurement errors, the authors developed a method to determine sensor response time in situ, using an established process for correcting sensor response time errors. This method requires a timestamp associated with each observation. The response time parameter (τ) was determined by correcting consecutive profiles taken in opposite directions using a range of possible values and finding the minimum root-mean-square-difference between them (Figure 1). In light of these findings, future oxygen measurements from Argo floats should be transmitted with time stamps for a calibration period during which up- and downcasts are recorded to facilitate response time correction. The method developed here will contribute to more accurate measurement of dissolved oxygen, thus improving the quality of derived quantities such as primary productivity.

Authors
Christopher Gordon (Dalhousie University)
Katja Fennel (Dalhousie University)
Clark Richards (Fisheries and Oceans Canada)
Nick Shay (University of Miami)
Jodi Brewster (University of Miami)

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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