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Ocean Carbon & Biogeochemistry

Studying marine ecosystems and biogeochemical cycles in the face of environmental change

Author Archive for mmaheigan

Ocean Sciences Postdoctoral Research Fellowships (OCE-PRF)

Posted by mmaheigan

· Friday, December 4th, 2020

Click for full details: Program Solicitation NSF 21-538

Full Proposal Target Date
March 3, 2021
November 12, 2021
Second Friday in November, Annually Thereafter

SYNOPSIS
The Division of Ocean Sciences (OCE) offers postdoctoral research fellowships (PRF) to provide opportunities for scientists early in their careers to work within and across traditional disciplinary lines, develop partnerships, and avail themselves of unique research resources, sites and facilities. The fellowship program is intended to provide beginning investigators of significant potential with experiences that will establish them in positions of leadership in the scientific community. During tenure, Fellows affiliate with a host research organization(s) and conduct research on topics supported by OCE. Fellowships will include participation in a professional development program that emphasizes development of mentoring skills and that coordinates the involvement of Fellows in conferences and activities that are focused on increasing the engagement of underrepresented groups in science, technology, engineering, and mathematics (STEM). Applicants must be U.S. citizens, nationals or permanent residents. Applicants who are women, veterans, persons with disabilities, and underrepresented minorities in STEM, or who have attended community colleges and minority-serving institutions (e.g. Historically Black Colleges and Universities, Tribal Colleges and Universities, Hispanic Serving Institutions, Alaska Native Serving Institutions, and Hawaiian Native and Pacific Islander Serving Institutions) are especially encouraged to apply.

What Has Been Funded (Recent Awards Made Through This Program, with Abstracts)

Map of Recent Awards Made Through This Program

Cognizant Program Officer(s):
See program website for any updates to the points of contact.

Elizabeth L. Rom, telephone: (703) 292-7709, email: elrom@nsf.gov
Henrietta N. Edmonds, telephone: (703) 292-7427, email: hedmonds@nsf.gov
Joaquín Martínez Martínez, telephone: (703) 292-8580, email: jmartine@nsf.gov
Daniel C. McCorkle, telephone: (703) 292-4543, email: dmccorkl@nsf.gov
Dana K. Savidge, telephone: (703) 292-4897, email: dsavidge@nsf.gov

How zooplankton control carbon export in the Southern Ocean

Posted by mmaheigan

· Thursday, December 3rd, 2020

The Southern Ocean exhibits an inverse relationship between surface primary production and export flux out of the euphotic zone. The causes of this production-export decoupling are still under debate. A recently published mini review in Frontiers in Marine Science focused on zooplankton, an important component of Southern Ocean food webs and the biological pump. The authors compared carbon export regimes from the naturally iron-fertilised Kerguelen Plateau (high surface production, but generally low export) with the iron-limited and less productive high nutrient, low chlorophyll (HNLC) waters south of Australia, where carbon export is relatively high.

Figure 1: The role of zooplankton in establishing the characteristic export regimes at two sites in the Southern Ocean, (a) the highly productive northern Kerguelen Plateau, which exhibits low export, and (b) the iron-limited waters south of Australia with low production, but relatively high carbon export.

Size structure and zooplankton grazing pressure are found to shape carbon export at both sites. On the Kerguelen Plateau, a large size spectrum of zooplankton acts as “gate-keeper” to the mesopelagic by significantly reducing the sinking flux of phytoaggregates, which establishes the characteristic low export regime. In the HNLC waters, however, the zooplankton community is low in biomass and grazes predominantly on smaller particles, which leaves the larger particles for export and leads to relatively high export flux.

Gaps in knowledge related to insufficient seasonal data coverage, understudied carbon flux pathways, and associated mesopelagic processes limit our current understanding of carbon transfer through the water column and export. More integrated data collection efforts, including the use of autonomous profiling floats (e.g., BGC-Argo), stationary moorings, etc., will improve seasonal carbon flux data coverage, thus enabling more reliable estimation of carbon export and storage in the Southern Ocean and improved projection of future changes in carbon uptake and atmospheric carbon dioxide levels.

Authors:
Svenja Halfter (University of Tasmania)
Emma Cavan (Imperial College London)
Ruth Eriksen (CSIRO)
Kerrie Swadling (University of Tasmania)
Philip Boyd (University of Tasmania)

Water clarity impacts temperature and biogeochemistry in Chesapeake Bay

Posted by mmaheigan

· Thursday, December 3rd, 2020

Estuarine water clarity is determined by suspended materials in the water, including colored dissolved organic matter, phytoplankton, sediment, and detritus. These constituents directly affect temperature because when water is opaque, sunlight heats only the shallowest layers near the surface, but when water is clear, sunlight can penetrate deeper, warming the waters below the surface. Despite the importance of accurately predicting temperature variability, many numerical modeling studies do not adequately parameterize this fundamental relationship between water clarity and temperature.

In a recent study published in Estuaries and Coasts, the authors quantified the impact of a more realistic representation of water clarity in a hydrodynamic-biogeochemical model of the Chesapeake Bay by comparing two simulations: (1) water clarity is constant in space and time for the calculation of solar heating vs. (2) water clarity varies with modeled concentrations of light-attenuating materials. In the variable water clarity simulation (2), the water is more opaque, particularly in the northern region of the Bay. During the spring and summer months, the lower water clarity in the northern Bay is associated with warmer surface temperatures and colder bottom temperatures. Warmer surface temperatures encourage phytoplankton growth and nutrient uptake near the head of the Bay, thus fewer nutrients are transported downstream. These conditions are exacerbated during high-river flow years, when differences in temperature, nutrients, phytoplankton, and zooplankton extend further seaward.

Figure 1: Top row: Difference in the light attenuation coefficient for shortwave heating, kh[m-1] (variable minus constant light attenuation simulation). June, July, and August average for (A) 2001, (B) average of 2001-2005, and (C) 2003; difference in bottom temperatures [oC] (variable minus constant). Bottom row: Difference in June, July, and August average bottom temperature for (D) 2001, (E) average of 2001-2005, and (F) 2003. Data for 2001 are representative of low river discharge, and 2003 are representative high river discharge years.

This work demonstrates that a constant light attenuation scheme for heating calculations in coupled hydrodynamic-biogeochemical models underestimates temperature variability, both temporally and spatially. This is an important finding for researchers who use models to predict future temperature variability and associated impacts on biogeochemistry and species habitability.

Authors:
Grace E. Kim (NASA, Goddard Space Flight Center)
Pierre St-Laurent (VIMS, William & Mary)
Marjorie A.M. Friedrichs (VIMS, William & Mary)
Antonio Mannino (NASA, Goddard Space Flight Center)

New trace gas paper!

Posted by mmaheigan

· Tuesday, December 1st, 2020

New paper inspired by discussions at OCB workshop on oceanic methane and nitrous oxide: Ideas and perspectives: A strategic assessment of methane and nitrous oxide measurements in the marine environment

Wilson, S. T., Al-Haj, A. N., Bourbonnais, A., Frey, C., Fulweiler, R. W., Kessler, J. D., Marchant, H. K., Milucka, J., Ray, N. E., Suntharalingham, P., Thornton, B. F., Upstill-Goddard, R. C., Weber, T. S., Arévalo-Martínez, D. L., Bange, H. W., Benway, H. M., Bianchi, D., Borges, A. V., Chang, B. X., Crill, P. M., del Valle, D. A., Farías, L., Joye, S. B., Kock, A., Labidi, J., Manning, C. C., Pohlman, J. W., Rehder, G., Sparrow, K. J., Tortell, P. D., Treude, T., Valentine, D. L., Ward, B. B., Yang, S., and Yurganov, L. N.: Ideas and perspectives: A strategic assessment of methane and nitrous oxide measurements in the marine environment, Biogeosciences, 17, 5809–5828, https://doi.org/10.5194/bg-17-5809-2020, 2020.

OCB Webinar Series

Posted by mmaheigan

· Tuesday, December 1st, 2020

OCB is extending the series - now accepting new titles and abstracts. Click to submit

Upcoming

DATE

THEME

SPEAKER(S)

TITLE(S)

15 December 12 pm (EST)

Spatial and temporal perspectives on the role of rivers in the Arctic coastal carbon cycle

Andrea Pain
(UMCES Horn Point)

Riverine export of carbon and nutrients from deglaciating Arctic landscapes: Implications for past and future climate transitions

Alexander Polukhin
(Shirshov Institute of Oceanology RAS, Moscow, Russia)

Carbonate system changes in the Russian Arctic Seas

We record and share videos below and on our YouTube channel to accommodate those who cannot participate in real time.

Use the Twitter hashtag #OCBwebinar to join and follow the discussion.

The OCB webinar series spans diverse science across OCB’s current research priorities.

Recent Webinars - Watch Now

DATE	THEME	SPEAKER(S)	TITLE(S)	Authors
17-Nov	EXPORTS: Field Campaign and Project Updates	Dave Siegel (UCSB)	Introduction
			Q&A session
		Jason Graff (OSU), Sasha Kramer (UCSB)	Phytoplankton community structure	Jason Graff (OSU), Erin Jones (URI), Lee Karp-Boss (UMaine), Sasha Kramer (UCSB), Collin Roesler (Bowdoin), Tatiana Rynearson (URI), Heidi Sosik (WHOI)
		Melanie Feen (URI), Meredith Meyer (UNC), Shannon Burns (USF)	Production/Diel Productivity	Melanie Feen (URI), Meredith Meyer (UNC), Shannon Burns (USF), Adrian Marchetti (UNC), Bethany Jenkins (URI), David Roo Nicholson (WHOI), Heather McNair (URI), James Fox(OSU), Kim Halsey (OSU), Kristen Buck (USF), Salvatore Caprara (USF), Mark Brzezinski (UCSB), Melissa Omand (URI), Mike Behrenfeld (OSU), Sarah Lerch (URI), Shawnee Traylor (WHOI/MIT), Susanne Menden-Deuer (URI), Weida Gong (UNC)
		Karen Stamieszkin (VIMS)	Mesozooplankton	Deborah Steinberg (VIMS), Amy Maas (BIOS), Karen Stamieszkin (VIMS), Joe Cope (VIMS), Andrea Miccoli, (ex-BIOS) Chandler Countryman (UGA), C. Carlson (UCSB), C. Durkin (MLML), M. Omand (URI)
		Brandon Stephens (UCSB), Garrett Sharpe (UNC)	Microbial processing	Brandon Stephens (UCSB), Garrett Sharpe (UNC), Craig Carlson (UCSB), Scott Gifford (UNC)
		Sarah Lerch (URI)	Food web synthesis	Heather McNair (URI), Sarah Lerch (URI), James Fox (OSU), Meredith Meyer (UNC), Amy Maas (BIOS), Tatiana Rynearson (URI), Acacia Zhao (UNC) , Alex Niebergall (Duke), Alyson Santoro (UCSB), Annie Bodel, Ben Van Mooy (WHOI), Brandon Stephens (UCSB), Brian Popp (UHawaii), Claudia Benitez-Nelson (USC), Colleen Durkin (MLML), Craig Carlson (UCSB), Dave Siegel (UCSB), Elisa Romanelli (UCSB), Eric D'Asaro (UW), Erin Jones (URI), Ewelina Rubin (URI), Garrett Sharpe (UNC), Heidi Sosik (WHOI), Henry Holm (WHOI), Hilary Close (UMiami), Jason Graff (OSU), Bethany Jenkins (URI), Kana Yamamoto (UCSB), Karen Stamieszkin (VIMS), Kristen Buck (USF), Kristofer Gomes (URI), Lee Karp-Boss (UMaine), Adrian Marchetti (UNC), Mark Brzezinski (UCSB), Meg Estapa (UMaine), Melanie Cohn (UNC), Melissa Duhaime (UMichigan), Susanne Menden-Deuer(URI), Nicola Paul (UCSB), David Roo Nicholson (WHOI), Salvatore Caprara (USF), Sasha Kramer (UCSB), Scott Gifford (UNC), Shannon Burns (USF), Victoria Fulfer (URI), Weida Gong (UNC)
			Q&A session
		Andrew McDonnell (UAlaska), Xiaodong Zhang (USM)	Particle size distribution	Xiaodong Zhang (USM), Lianbo Hu (UND), Yuanheng Xiong (UNDakota - UND), Deric Gray (NRL), Yannick Huot (USherbrooke), Andrew McDonnell (UAlaska), Rachel Lekanoff(UAlaska), Jessica Pretty (UAlaska), Brita Irving (UAlaska), Dave Siegel (UCSB), Norm Nelson (UCSB), Lee Karp-Boss (UMaine), Emmanuel Boss (UMaine), Guillaume Bourdin (UMaine), Nils Haentjens (UMaine), Marc Picheral (CNRS, LOV), Lionel Guidi (CNRS, LOV)
		Hilary Close (UMiami)	Vertical sinking and processing of particulate organic matter (POM)	Hilary Close (UMiami), Meg Estapa (Univ. Maine), Vinicius Amaral (UCSC), Olivier Marchal (WHOI), Phoebe Lam (UC Santa Cruz), Elisa Romanelli (UCSB), Uta Passow (Memorial UNewfoundland), Muntsa Roca Marti (WHOI), Ken Buesseler (WHOI), Claudia Benitez-Nelson (USC), Colleen Durkin (MLML), Melissa Omand (URI), Annie Bodel (MLML), Alyson Santoro (UCSB), Pat Kelley (URI), Paul Wojtal (UMiami), Shannon Doherty (UMiami), Brian Popp (UHawaii), Connor Shea (UHawaii),
		Muntsa Roca Martí (WHOI)	Radiochemical assessments of flux	Muntsa Roca Martí (WHOI), Ken Buesseler (WHOI), Claudia Benitez-Nelson (USC), Laure Resplandy (Princeton)
		Alex Niebergall (Duke), Shawnee Traylor (WHOI/MIT), Roo Nicholson (WHOI)	Biogeochemical mass balances	Alex Niebergall (Duke), Shawnee Traylor (WHOI/MIT), Roo Nicholson (WHOI), Andrea Fassbender (NOAA PMEL), Muntsa Roca Marti (WHOI), Brandon Stevens (UCSB), Huang, Adrian Marchetti (UNC), Meredith Meyer (UNC), Melissa Omand (URI), Melanie Feen (URI), Nicolas Cassar (Duke), Yibin Huang (UCSC)
			Q&A session
		Dave Siegel (UCSB)	Wrap up

DATE	THEME	SPEAKER(S)	TITLE(S)	SESSION CHAIR(S)
3-Nov	Productivity and marine snow dynamics: Novel approaches and measurements of the biological pump	Amanda Timmerman (UCSD)	Fronts implicated as the missing mechanism driving phytoplankton variability in the iron-limited subarctic NE Pacific	Reimers
		Klas Ove Möller (Institute of Coastal Research, HZG)	Sinking vs. remineralisation: Active controls of zooplankton on marine snow dynamics

DATE	THEME	SPEAKER(S)	TITLE(S)	SESSION CHAIR(S)
6-Oct	New insights on the marine nitrogen cycle	Clara A. Fuchsman (UMCES Horn Point Laboratory)	Quantification of organic matter sources for N₂ production in oxygen minimum zones	Granger
		Francisco J. Cervantes (Universidad Nacional Autónoma de México)	Novel microbial processes potentially interconnecting global biogeochemical cycles in marine environments

DATE	THEME	SPEAKER(S)	TITLE(S)	SESSION CHAIR(S)
8-Sep	Changes in the ocean's organic carbon cycle	Cristina Romera Castillo (Instituto de Ciencias del Mar-CSIC)	Net production of dissolved organic carbon in the deep ocean	Rafter, Hood
		Emma Cavan (Imperial College London)	Ecological feedbacks to the ocean organic carbon cycle: Fishing and climate change

25-Aug	Modeling and machine learning approaches to study climate, carbon, and the ocean	Katarzyna (Kasia) Tokarska (ETH Zürich)	Climate-carbon response: carbon budgets in overshoot scenarios, and in high warming models	Long, Stock
		Christopher Holder (Johns Hopkins University)	Machine Learning and Some Potential Uses in Oceanography

11-Aug

Advancing understanding of biological feedbacks on ocean biogeochemistry

Emily Zakem (University of Southern California)

Redox-informed models of global biogeochemical cycles

Coles, Maas

Severine Martini (Mediterranean Institute of Oceanography)

Shedding light (literally!) on biological carbon pump

28-Jul	Physical drivers of marine biogeochemistry and ecology	Mara Freilich (MIT-WHOI Joint Program)	Phytoplankton community structure in response to meso- and submeso-scale physics	Palter, Friedrichs
		Natalie Freeman (University of Colorado Boulder)	On the recent increase in surface silicate-to-nitrate availability in the southern Drake Passage

14-July	Physical and biogeochemical processes that drive the biological pump	Hilary Palevsky (Boston College, Department of Earth and Environmental Sciences)	The influence of winter ventilation on the ocean’s biological carbon pump	Bushinsky, Fassbender
		Joan Llort (Barcelona Supercomputing Centre)	The four dimensions of the biological carbon pump

30-Jun

Space-based ocean measurements

Jeremy Werdell (NASA)

Socially distant by design: How the evolution of ocean color remote sensing contributes to aquatic biological and biogeochemical studies (NASA PACE)

Benway

PACE Mission Survey

Posted by mmaheigan

· Tuesday, November 24th, 2020

The PACE mission, a hyper-spectral mission spanning from the UV to the NIR, is preparing for launch in 2023 and in anticipation we would like to develop radiative products that will be most useful for the community. To guide this effort, we are asking potential PACE data users to provide input on what products of the list below (or others) they would like to see produced from PACE, as the choice of products that will be considered for production will depend on the level of interest with the user community, in addition to considerations such as the degree to which achievable accuracy compares to needed accuracy, the feasibility of implementation, computational requirements, and the availability of data production and distribution resources.

This survey is the brainchild of Emmanuel Boss and Robert Frouin who are members of the PACE Science and Application Team and are funded to work with NASA’s OBPG on these products. We will wrap up this survey and share the results at the end of November, 2020.

Some background
In 2015 the Plymouth Marine Laboratory (PML) requested feedback from the community on the adequacy of available product including importance, usage and accuracy and additional features users felt were needed. 63 members of the community responded and their replies are compiled in Frouin et al., 2018 (doi: 10.3389/fmars.2018.00003).

Based on this survey and additional considerations a list of new products was compiled:
• Sub-surface planar and scalar PAR (as opposed to above the surface).
• Fraction of PAR absorbed by phytoplankton (APAR).
• Diffuse fraction of total irradiance (average cosine of light field just below the surface).
• Spectral planar and scalar irradiance.
• Spectral diffuse attenuation coefficient for downward irradiance,
• Surface albedo (ratio of planar upward irradiance to downward planar irradiance just above the ocean surface).
• UV-A, UV-B planar and scalar irradiance (with photon and energy units).
• Products without gaps (in space/time) to provide boundary conditions to models.
• Upper-ocean heating profile.
• Diurnal distribution of PAR and its attenuation.
• Averaged mixed-layer PAR.
• Under-ice light fields.

Current products that are likely to be available for PACE

NASA’s Ocean Biology Processing Group (OBPG) currently produces the following products associated with radiometry, from a host of active and legacy multispectral satellite sensors (based on https://oceancolor.gsfc.nasa.gov/product_status/):

Rrs – Water leaving radiance normalized by surface irradiance calculated as TOA irradiance scaled by atmospheric transmittance and solar geometry and corrected for BRDF effects and changes in earth-sun distance. Unit – [sr-1]

PAR – Daily average downward planar photosynthetically available radiation above surface. Unit – [Einstein m-2 day-1]

iPAR – Instantaneous clear sky downward planar photosynthetically available radiation just above surface at the time of satellite passage. Unit – [Einstein m-2 s-1]

Kd490 – Diffuse attenuation coefficient of downwelling planar irradiance at 490nm. Unit – [m-1]

Euphotic depth – Euphotic depth (defined as the depth of the 1% planar PAR irradiance depth relative to its surface value (0-). Unit – [m]

Tiny phytoplankton seen from space

Posted by mmaheigan

· Thursday, November 19th, 2020

Picophytoplankton, the smallest phytoplankton on Earth, are dominant in over half of the global surface ocean, growing in low-nutrient “ocean deserts” where diatoms and other large phytoplankton have difficult to thrive. Despite their small size, picophytoplankton collectively account for well over 50% of primary production in oligotrophic waters, thus playing a major role in sustaining marine food webs.

In a recent paper published in Optics Express, the authors use satellite-detected ocean color (namely remote-sensing reflectance, R_rs(λ)) and sea surface temperature to estimate the abundance of the three picophytoplankton groups—the cyanobacteria Prochlorococcus and Synechococcus, and autotrophic picoeukaryotes. The authors analysed R_rs(λ) spectra using principal component analysis, and principal component scores and SST were used in the predictive models. Then, they trained and independently evaluated the models with in-situ data from the Atlantic Ocean (Atlantic Meridional Transect cruises). This approach allows for the satellite detection of the succession of species across ocean oligotrophic ecosystem boundaries, where these cells are most abundant (Figure 1).

Figure 1. Cell abundances of the three major picophytoplankton groups (the cyanobacteria Prochlorococcus and Synechococcus, and a collective group of autotrophic picoeukaryotes) in surface waters of the Atlantic Ocean. Abundances are shown for the dominant group in terms of total biovolume (converted from cell abundance).

Since these organisms can be used as proxies for marine ecosystem boundaries, this method can be used in studies of climate and ecosystem change, as it allows a synoptic observation of changes in picophytoplankton distributions over time and space. For exploring spectral features in hyperspectral R_rs(λ) data, the implementation of this model using data from future hyperspectral satellite instruments such as NASA PACE’s Ocean Color Instrument (OCI) will extend our knowledge about the distribution of these ecologically relevant phytoplankton taxa. These observations are crucial for broad comprehension of the effects of climate change in the expansion or shifts in ocean ecosystems.

Authors:
Priscila K. Lange (NASA Goddard Space Flight Center / Universities Space Research Association / Blue Marble Space Institute of Science)
Jeremy Werdell (NASA Goddard Space Flight Center)
Zachary K. Erickson (NASA Goddard Space Flight Center)
Giorgio Dall’Olmo (Plymouth Marine Laboratory)
Robert J. W. Brewin (University of Exeter)
Mikhail V. Zubkov (Scottish Association for Marine Science)
Glen A. Tarran (Plymouth Marine Laboratory)
Heather A. Bouman (University of Oxford)
Wayne H. Slade (Sequoia Scientific, Inc)
Susanne E. Craig (NASA Goddard Space Flight Center / Universities Space Research Association)
Nicole J. Poulton (Bigelow Laboratory for Ocean Sciences)
Astrid Bracher (Alfred-Wegener-Institute Helmholtz Center for Polar and Marine Research / University of Bremen)
Michael W. Lomas (Bigelow Laboratory for Ocean Sciences)
Ivona Cetinić (NASA Goddard Space Flight Center / Universities Space Research Association)

A new Regional Earth System Model of the Mediterranean Sea biogeochemical dynamics

Posted by mmaheigan

· Thursday, November 19th, 2020

The Mediterranean Sea is a semi-enclosed mid-latitude oligotrophic basin with a lower net primary production than the global ocean. A west-east productivity trophic gradient results from the superposition of biogeochemical and physical processes, including the biological pump and associated carbon and nutrient (nitrogen, phosphorus) fluxes, the spatial asymmetric distribution of nutrient sources (rivers, atmospheric deposition, coastal upwelling, etc.), the estuarine inverse circulation associated with the inflow of Atlantic water through the Gibraltar Strait. The complex and highly variable interface between land and sea throughout this basin add a further layer of complexity in the Mediterranean oceanic and atmospheric circulation and on the associated biogeochemistry dynamics, emphasizing the need for high-resolution truly integrated Regional Earth System Models to track and understand fine-scale processes and ecosystem dynamics.

In a recent paper published in the Journal of Advances in Modeling Earth System, the authors introduced a new version of the Regional Earth System model RegCM-ES and evaluated its performance in the Mediterranean region. RegCM-ES fully integrates the regional climate model RegCM4, the land surface scheme CLM4.5 (Community Land Model), the river routing model HD (Hydrological Discharge Model), the ocean model MITgcm (MIT General Circulation model) and the Biogeochemical Flux Model BFM.

A comparison with available observations has shown that RegCM-ES was able to capture the mean climate of the region and to reproduce horizontal and vertical patterns of chlorophyll-a and PO₄(the limiting nutrient in the basin) (Figure 1). The same comparison revealed a systematic underestimation of simulated dissolved oxygen (which will be fixed by the use of a new parametrization of oxygen solubility), and an overestimation of NO₃, possibly due to uncertainties in initial and boundary conditions (mostly traced to river and Dardanelles nutrient discharges) and an overly vigorous vertical mixing simulated by the ocean model in some parts of the Basin.

Figure.1 Distributions of chlorophyll-a mg/m³ (top) and PO₄ mmol/m³ (bottom) in the Mediterranean Sea as simulated by RegCM-ES.

Overall, this analysis has demonstrated that RegCM-ES has the capabilities required to become a powerful tool for studying regional dynamics and impacts of climate change on the Mediterranean Sea and other ocean basins around the world.

Authors:
Marco Reale (Abdus Salam International Centre for theoretical physics-ICTP, National Institute of Oceanography and Experimental Geophysics-OGS)
Filippo Giorgi (Abdus Salam International Centre for theoretical physics-ICTP)
Cosimo Solidoro (National Institute of Oceanography and Experimental Geophysics-OGS)
Valeria Di Biagio (National Institute of Oceanography and Experimental Geophysics-OGS)
Fabio Di Sante (Abdus Salam International Centre for theoretical physics-ICTP)
Laura Mariotti (National Institute of Oceanography and Experimental Geophysics-OGS)
Riccardo Farneti (Abdus Salam International Centre for theoretical physics-ICTP)
Gianmaria Sannino (Italian National Agency for New Technologies, Energy and Sustainable Economic Development-ENEA)

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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