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Archive for surface ocean

pH: the secrets that you keep

Posted by mmaheigan 
· Monday, September 20th, 2021 

The Intergovernmental Panel on Climate Change (IPCC) defines ocean acidification as “a reduction in pH of the ocean over an extended period, typically decades or longer, caused primarily by the uptake of carbon dioxide (CO2) from the atmosphere” (Rhein et al., 2013, p. 295). Does this mean that a greater change in pH at the ocean surface relative to the subsurface, or at one location relative to another, always indicates greater acidification? Based on this IPCC definition of ocean acidification, the answer is yes. But does that make sense?

Seawater pH is the negative base 10 logarithm of the seawater’s hydrogen ion concentration ([H+]) and is a useful way to display a wide range of [H+] in a compact form. A change in pH reflects a relative change in [H+]. Thus, anytime we speak of pH changes, we are really referring to a relative change in the chemical species of interest ([H+]). On the other hand, changes in all the other carbonate system variables that we measure are usually absolute. This characteristic of pH can lead to ambiguity in the interpretation and presentation of rates and patterns of change. Improved understanding comes from also studying changes in [H+], which can reveal aspects that studying changes in pH alone may conceal or overemphasize.

A recent Biogeosciences article reviewed the history leading to this unintuitive relationship between changes in pH and changes in [H+]. The article provides three real-world examples to display how examining pH changes alone can hide the ocean acidification signals of interest (Figure 1). These examples highlight potential challenges associated with comparing surface and subsurface pH changes across ocean domains without accounting for differences in the initial pH values. The authors recommend reporting both pH and [H+] in studies that assess changes in ocean chemistry to improve the clarity of ocean acidification research.

Figure Caption: Data used in this figure come from the GFDL ESM2M model for the combined historical and RCP8.5 experiments. Top: the 1950s surface ocean (left) pH and (right) [H+]. Bottom: the 1950s to 2090s change (Δ) in surface ocean (left) pH and (right) [H+]. The color bar for ΔpH is reversed to ease comparison with patterns of Δ[H+]

Authors:
Andrea J. Fassbender (NOAA Pacific Marine Environmental Laboratory)
Andrew G. Dickson (Scripps Institution of Oceanography, University of California, San Diego)
James C. Orr (LSCE/IPSL, Laboratoire des Sciences du Climat et de l’Environnement)

Exploiting phytoplankton as a biosensor for nutrient limitation

Posted by mmaheigan 
· Wednesday, September 15th, 2021 

In the surface ocean, phytoplankton growth is often limited by a scarcity of key nutrients such as nitrogen, phosphorus, and iron. While this is important, there are methodological and conceptual difficulties in characterizing these nutrient limitations.

A recent paper published in Science Magazine leveraged a global metagenomic dataset from Bio-GO-SHIP to address these challenges. The authors characterized the abundance of genes that confer adaptations to nutrient limitation within the picocyanobacteria Prochlorococcus. Using the relative abundance of these genes as an indicator of nutrient limitation allowed the authors to capture expected regions of nutrient limitation, and novel regions that had not previously been studied. This gene-derived indicator of nutrient limitation matched previous methods of assessing nutrient limitation, such as bottle incubation experiments.

These findings have important implications for the global ocean. Characterizing the impact of nutrient limitation on primary production is especially critical in light of future stratification driven by climate change. In addition, this novel methodological approach allows scientists to use microbial communities as an eco-genomic biosensor of adaptation to changing nutrient regimes. For instance, future studies of coastal microbes or other ecosystems may help communities and environmental managers better understand how local microbial populations are adapting to climate change.

 

Watch an illustrated video overview of this research

Authors:
Lucas J. Ustick, Alyse A. Larkin, Catherine A. Garcia, Nathan S. Garcia, Melissa L. Brock, Jenna A. Lee, Nicola A. Wiseman, J. Keith Moore, Adam C. Martiny
(all University of California, Irvine)

How atmospheric and oceanographic forcing impact the carbon sequestration in an ultra-oligotrophic marine system

Posted by mmaheigan 
· Wednesday, August 11th, 2021 

Sinking particles are a critical conduit for the export of material from the surface to the deep ocean. Despite their importance in oceanic carbon cycling, little is known about the composition and seasonal variability of sinking particles which reach abyssal depths. Oligotrophic waters cover ~75% of the ocean surface and contribute over 30% of the global marine carbon fixation. Understanding the processes that control carbon export to the deep oligotrophic areas is crucial to better characterize the strength and efficiency of the biological pump as well as to project the response of these systems to climate fluctuations and anthropogenic perturbations.

In a recent study published in Frontiers in Earth Science, authors synthesized data from atmospheric and oceanographic parameters, together with main mass components, and stable isotope and source-specific lipid biomarker composition of sinking particles collected in the deep Eastern Mediterranean Sea (4285m, Ierapetra Basin) for a three-year period (June 2010-June 2013). In addition, this study compared the sinking particulate flux data with previously reported deep-sea surface sediments from the study area to shed light on the benthic–pelagic coupling.

Figure Caption: a) Biplot of net primary productivity vs export efficiency (top and bottom horizontal dashed lines indicate threshold for high and low export efficiency regimes). b) Biplot of POC-normalized concentrations of terrestrial vs. phytoplankton-derived lipid biomarkers of the sinking particles collected in the deep Eastern Mediterranean Sea (Ierapetra Basin, NW Levantine Basin) from June 2010–June 2013, and surface sediments collected from January 2007 to June 2012 in the study area.

Both seasonal and episodic pulses are crucial for POC export to the deep Eastern Mediterranean Sea. POC fluxes peaked in spring April–May 2012 (12.2 mg m−2 d−1) related with extreme atmospheric forcing. Overall, summer particle export fuels more efficient carbon sequestration than the other seasons. The results of this study highlight that the combination of extreme weather events and aerosol deposition can trigger an influx of both marine labile carbon and anthropogenic compounds to the deep. Finally, the comparison of the sinking particles flux data with surface sediments revealed an isotopic discrimination, as well as a preferential degradation of labile organic matter during deposition and burial, along with higher preservation of land-derived POC in the underlying sediments. This study provides key knowledge to better understand the export, fate and preservation vs. degradation of organic carbon, and for modeling the organic carbon burial rates in the Mediterranean Sea.

 

Authors:
Rut Pedrosa-Pamies (The Ecosystems Center, Marine Biological Laboratory, US; Research Group in Marine Geosciences, University of Barcelona, Spain)
Constantine Parinos (Institute of Oceanography, Hellenic Centre for Marine Research, Greece)
Anna Sanchez-Vidal (Group in Marine Geosciences, University of Barcelona, Spain)
Antoni Calafat (Group in Marine Geosciences, University of Barcelona, Spain)
Miquel Canals (Group in Marine Geosciences, University of Barcelona, Spain)
Dimitris Velaoras (Institute of Oceanography, Hellenic Centre for Marine Research, Greece)
Nikolaos Mihalopoulos (Environmental Chemical Processes Laboratory, University of Crete; National Observatory of Athens, Greece)
Maria Kanakidou (Environmental Chemical Processes Laboratory, University of Crete Greece)
Nikolaos Lampadariou (Institute of Oceanography, Hellenic Centre for Marine Research, Greece)
Alexandra Gogou (Institute of Oceanography, Hellenic Centre for Marine Research, Greece)

A new proxy for ocean iron bioavailability

Posted by mmaheigan 
· Monday, July 26th, 2021 

In many oceanic regions, iron exerts strong control on phytoplankton growth, ecosystem structure and carbon cycling. Yet, iron bioavailability and uptake rates by phytoplankton in the ocean are poorly constrained.

Recently, Shaked et al. (2020) (see GEOTRACES highlight), established a new approach for quantifying the availability of dissolved Fe (dFe) in natural seawater based on its uptake kinetics by Fe-limited cultured phytoplankton. In a follow up study published in GBC, this approach was extended to in situ phytoplankton, establishing a standardized proxy for dFe bioavailability in low-Fe ocean regions.

As explained in the short video lecture above, Yeala Shaked, Ben Twining, and their colleagues have analyzed large datasets collected during 10 research cruises (including 3 GEOTRACES section and process cruises) in multiple ocean regions. Dissolved Fe bioavailability was estimated through single cell Fe uptake rates, calculated by combining measured Fe contents of individual phytoplankton cells collected with concurrently-measured dFe concentrations, as well as modeled growth rates (Figure). Then the authors applied this proxy for: a) comparing dFe bioavailability among organisms and regions; b) calculating dFe uptake rates and residence times in low-Fe oceanic regions; and c) constraining Fe uptake parameters of earth system models to better predict ocean productivity in response to climate-change.

The data suggest that dFe species are highly available in low-Fe settings, likely due to photochemical reactions in sunlit waters.

Figure 1: The new bioavailability proxy (an uptake rate constant-kin-app) was calculated for ~1000 single cells from multiple ocean regions. For each cell, the iron quota was measured with synchrotron x-ray fluorescence (left panel), a growth rate was estimated from the PISCES model for the corresponding phytoplankton group (right panel), and the dissolved Fe concentration was measured concurrently (middle panel).

Authors:
Y. Shaked (Hebrew University and Interuniversity Institute for Marine Sciences)
B.S. Twining (Bigelow Lab)
A. Tagliabue (University of Liverpool)
M.T. Maldonado (University of British Columbia)
K.N. Buck (University of South Florida)
T. Mellett (University of South Florida)

References:
Shaked, Y., Twining, B. S., Tagliabue, A., & Maldonado, M. T. (2021). Probing the bioavailability of dissolved iron to marine eukaryotic phytoplankton using in situ single cell iron quotas. Global Biogeochemical Cycles, e2021GB006979. https://doi.org/10.1029/2021GB006979

Shaked, Y., Buck, K. N., Mellett, T., & Maldonado, M. T. (2020). Insights into the bioavailability of oceanic dissolved Fe from phytoplankton uptake kinetics. The ISME Journal, 1–12. https://doi.org/10.1038/s41396-020-0597-3

 

Joint highlight with GEOTRACES – read here.

Acidity across the interface from the ocean surface to sea spray aerosol

Posted by mmaheigan 
· Wednesday, March 31st, 2021 

The pH of aerosols controls their impact on climate and human health. Sea spray aerosols are one of the largest sources of aerosols globally by mass, yet it has been challenging to measure the pH of fresh sea spray aerosols in the past. A recent study published in PNAS measured sea spray aerosols under controlled conditions, during a sampling intensive called SeaSCAPE, and optimized a pH paper-based technique to measure the aerosol acidity. The authors found that fresh sea spray aerosols can be rapidly acidified by 4 to 6 orders of magnitude relative to the ocean. This acidification is caused by interaction with surrounding acidic gases, changes in relative humidity, and enhanced dissociation of organic acids within the aerosols. This is a critical finding since the pH of aerosols controls key atmospheric chemical reactions including sulfur dioxide oxidation to form particulate sulfate. The results are also important in light of the fact that enzyme activity has been observed in sea spray aerosols, and enzyme activity is pH dependent.

Figure 1. Acidity of nascent sea spray aerosols (SSA) compared to bulk ocean water measured during the 2019 SeaSCAPE sampling intensive. Background artwork by Nigella Hillgarth.

 

Authors
Kyle Angle (University of California, San Diego)
Daniel Crocker (University of California, San Diego)
Rebecca Simpson (University of California, San Diego)
Kathryn Mayer (University of California, San Diego)
Lauren Garofalo (Colorado State University, Fort Collins)
Alexia Moore (University of California, San Diego)
Stephanie Mora Garcia (University of California, San Diego)
Victor Or (University of California, San Diego)
Sudarshan Srinivasan (University of California, San Diego)
Mahum Farhan (University of California, San Diego)
Jonathan Sauer (University of California, San Diego)
Christopher Lee (University of California, San Diego)
Matson Pothier (Colorado State University, Fort Collins)
Delphine Farmer (Colorado State University, Fort Collins)
Todd Martz (University of California, San Diego)
Timothy Bertram (University of Wisconsin, Madison)
Christopher Cappa (University of California, Davis)
Kimberly Prather (University of California, San Diego)
Vicki Grassian (University of California, San Diego)

 

Joint post with Surface Ocean – Lower Atmosphere Study (SOLAS)

How environmental drivers regulated the long-term evolution of the biological pump

Posted by mmaheigan 
· Friday, January 22nd, 2021 

The marine biological pump (BP) plays a crucial role in regulating earth’s atmospheric oxygen and carbon dioxide levels by transferring carbon fixed by primary producers into the ocean interior and marine sediments, thereby controlling the habitability of our planet. The rise of multicellular life and eukaryotic algae in the ocean about 700 million years ago would likely have influenced the physical characteristics of oceanic aggregates (e.g., sinking rate), yet the magnitude of the impact this biological innovation had on the efficiency of BP is unknown.

Figure. 1. The impact of biological innovations (left) and environmental factors (atmospheric oxygen level and seawater temperature; right) on the efficiency of marine biological pump (BP). Temperatures are ocean surface temperatures (SST), and atmospheric pO2 is shown relative to the present atmospheric level (PAL). The BP efficiency is calculated as the fraction of carbon exported from the surface ocean that is delivered to the sediment-water interface. The results indicate that evolution of larger sized algae and zooplanktons has little influence on the long-term evolution of biological pump (left panel). The change in the atmospheric oxygen level and seawater surface temperature as environmental factors, on the other hand, have a stronger leverage on the efficiency of biological pump (right panel).

The authors of a recent paper in Nature Geoscience constructed a particle-based stochastic model to explore the change in the efficiency of the BP in response to biological and physical changes in the ocean over geologic time. The model calculates the age of organic particles in each aggregate based on their sinking rates, and considers the impact of primary producer cell size, aggregation, temperature, dust flux, biomineralization, ballasting by mineral phases, oxygen, and the fractal geometry (porosity) of aggregates. The model results demonstrate that while the rise of larger-sized eukaryotes led to an increase in the average sinking rate of oceanic aggregates, its impact on BP efficiency was minor. The evolution of zooplankton (with daily vertical migration in the water column) had a larger impact on the carbon transfer into the ocean interior. But results suggest that environmental factors most strongly affected the marine carbon pump efficiency. Specifically, increased ocean temperatures and greater atmospheric oxygen abundance led to a significant decrease in the efficiency of the BP. Cumulatively, these results suggest that while major biological innovations influenced the efficiency of BP, the long-term evolution of the marine carbon pump was primarily controlled by environmental drivers such as climate cooling and warming. By enhancing the rate of heterotrophic microbial degradation, our results suggest that the anthropogenically-driven global warming can result in a less efficient BP with reduced power of marine ecosystem in sequestering carbon from the atmosphere.

Authors:
Mojtaba Fakhraee (Yale University, Georgia Tech, and NASA Astrobiology Institute)
Noah J. Planavsky (Yale University, and NASA Astrobiology Institute)
Christopher T. Reinhard (Georgia Tech, and NASA Astrobiology Institute)

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 CO2 from 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)

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, Rrs(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 Rrs(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 Rrs(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)

 

Austral summer vertical migration patterns in Antarctic zooplankton

Posted by mmaheigan 
· Thursday, October 15th, 2020 

Sunrise and sunset are the main cues driving zooplankton diel vertical migration (DVM) throughout the world’s oceans. These marine animals balance the trade-off between feeding in surface waters at night and avoiding predation during the day at depth. Near-constant daylight during polar summer was assumed to dampen these daily migrations. In a recent paper published in Deep-Sea Research I, authors assessed austral summer DVM patterns for 15 taxa over a 9-year period. Despite up to 22 hours of sunlight, a diverse array of zooplankton – including copepods, krill, pteropods, and salps – continued DVM.

Figure caption: Mean day (orange) and night (blue) abundance of (A) the salp Salpa thompsoni, (B) the krill species Thysanoessa macrura, (C) the pteropod Limacina helicina, and (D) chaetognaths sampled at discrete depth intervals from 0-500m. Horizontal dashed lines indicate weighted mean depth (WMD). N:D is the night to day abundance ratio for 0-150 m. Error bars indicate one standard error. Sample size n = 12 to 22. Photos by Larry Madin, Miram Gleiber, and Kharis Schrage.

The Palmer Antarctica Long-Term Ecological Research (LTER) Program conducted this study using a MOCNESS (Multiple Opening/Closing Net and Environmental Sensing System) to collect depth-stratified samples west of the Antarctic Peninsula. The depth range of migrations during austral summer varied across taxa and with daylength and phytoplankton biomass and distribution. While most taxa continued some form of DVM, others (e.g., carnivores and detritivores) remained most abundant in the mesopelagic zone, regardless of photoperiod, which likely impacted the attenuation of vertical carbon flux. Given the observed differences in vertical distribution and migration behavior across taxa, ongoing changes in Antarctic zooplankton assemblages will likely impact carbon export pathways. More regional, taxon-specific studies such as this are needed to inform efforts to model zooplankton contributions to the biological carbon pump.

 

Authors:
John Conroy (VIMS, William & Mary)
Deborah Steinberg (VIMS, William & Mary)
Patricia Thibodeau (VIMS, William & Mary; currently University of Rhode Island)
Oscar Schofield (Rutgers University)

Marine heatwave implications for future phytoplankton blooms

Posted by mmaheigan 
· Thursday, October 15th, 2020 

Ocean temperature extreme events such as marine heatwaves are expected to intensify in coming decades due to anthropogenic warming. Although the effects of marine heatwaves on large plants and animals are becoming well documented, little is known about how these warming events will impact microbes that regulate key biogeochemical processes such as ocean carbon uptake and export, which represent important feedbacks on the global carbon cycle and climate.

Figure caption: Relationship between phytoplankton bloom response to marine heatwaves and background nitrate concentration in the 23 study regions. X-axis denotes the annual-mean sea-surface nitrate concentration based on the model simulation (1992-2014; OFAM3, blue) and the in situ climatology (WOA13, orange). Y-axis denotes the mean standardised anomalies (see Equation 1 of the paper) of simulated sea-surface phytoplankton nitrogen biomass (1992-2014; OFAM3, blue) and observed sea-surface chlorophyll a concentration (2002-2018; MODIS, orange) during the co-occurrence of phytoplankton blooms and marine heatwaves.

In a recent study published in Global Change Biology, authors combined model simulations and satellite observations in tropical and temperate oceanographic regions over recent decades to characterize marine heatwave impacts on phytoplankton blooms. The results reveal regionally‐coherent anomalies depicted by shallower surface mixed layers and lower surface nitrate concentrations during marine heatwaves, which counteract known light and nutrient limitation effects on phytoplankton growth, respectively (Figure 1). Consequently, phytoplankton bloom responses are mixed, but derive from the background nutrient conditions of a study region such that blooms are weaker (stronger) during marine heatwaves in nutrient-poor (nutrient-rich) waters.

Given the projected expansion of nutrient-poor waters in the 21st century ocean, the coming decades are likely to see an increased occurrence of weaker blooms during marine heatwaves, with implications for higher trophic levels and biogeochemical cycling of key elements.

Authors:
Hakase Hayashida (University of Tasmania)
Richard Matear (CSIRO)
Pete Strutton (University of Tasmania)

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