Whole-system metabolism and CO₂ fluxes in a Mediterranean Bay dominated by seagrass beds (Palma Bay, NW Mediterranean)

The relationship between whole-system metabolism estimates based on planktonic and benthic incubations (bare sediments and seagrass, Posidonia oceanica meadows), and CO2 fluxes across the air-sea interface were examined in the Bay of Palma (Mallorca, Spain) during two cruises in March and June 2002. Moreover, planktonic and benthic incubations were performed at monthly intervals from March 2001 to October 2002 in a seagrass vegetated area of the bay. From the annual study, results showed a contrast between the planktonic compartment, which was heterotrophic during most of the year, except for occasional bloom episodes, and the benthic compartment, which was slightly autotrophic. Whereas the seagrass community was autotrophic, the excess organic carbon production therein could only balance the excess respiration of the planktonic compartment in shallow waters (<10 m) relative to the maximum depth of the bay (55 m). This generated a horizontal gradient from autotrophic or balanced communities in the shallow, seagrass-covered areas of the bay, to strongly heterotrophic communities in deeper areas, consistent with the patterns of CO2 fields and fluxes across the bay observed during the two extensive cruises in 2002. Finally, dissolved inorganic carbon and oxygen budgets provided NEP estimates in fair agreement with those derived from direct metabolic estimates based on incubated samples over the Posidonia oceanica meadow

EPOCA/EUR-OCEANS data compilation on the biological and biogeochemical responses to ocean acidification

The uptake of anthropogenic CO2 by the oceans has led to a rise in the oceanic partial pressure of CO2, and to a decrease in pH and carbonate ion concentration. This modification of the marine carbonate system is referred to as ocean acidification. Numerous papers report the effects of ocean acidification on marine organisms and communities but few have provided details concerning full carbonate chemistry and complementary observations. Additionally, carbonate system variables are often reported in different units, calculated using different sets of dissociation constants and on different pH scales. Hence the direct comparison of experimental results has been problematic and often misleading. The need was identified to (1) gather data on carbonate chemistry, biological and biogeochemical properties, and other ancillary data from published experimental data, (2) transform the information into common framework, and (3) make data freely available. The present paper is the outcome of an effort to integrate ocean carbonate chemistry data from the literature which has been supported by the European Network of Excellence for Ocean Ecosystems Analysis (EUR-OCEANS) and the European Project on Ocean Acidification (EPOCA). A total of 185 papers were identified, 100 contained enough information to readily compute carbonate chemistry variables, and 81 data sets were archived at PANGAEA – The Publishing Network for Geoscientific & Environmental Data. This data compilation is regularly updated as an ongoing mission of EPOCA.

Whole-system metabolism and CO2 fluxes in a Mediterranean Bay dominated by seagrass beds (Palma Bay, NW Mediterranean)

Planktonic and benthic incubations (bare and Posidonia oceanica vegetated sediments) were performed at monthly intervals from March 2001 to October 2002 in a seagrass vegetated area of the Bay of Palma (Mallorca, Spain). Results showed a contrast between the planktonic compartment, which was on average near metabolic balance (-4.6 +/- 5.9 mmol O-2 m(-2) d(-1)) and the benthic compartment, which was autotrophic (17.6 +/- 8.5 mmol O-2 m(-2) d(-1)). During two cruises in March and June 2002, planktonic and benthic incubations were performed at several stations in the bay to estimate the whole-system metabolism and to examine its relationship with partial pressure of CO2 (pCO(2)) and apparent oxygen utilisation (AOU) spatial patterns. Moreover, during the second cruise, when the residence time of water was long enough, net ecosystem production (NEP) estimates based on incubations were compared, over the Posidonia oceanica meadow, to rates derived from dissolved inorganic carbon ! (DIC) and oxygen (O-2) mass balance budgets. These budgets provided NEP estimates in fair agreement with those derived from direct metabolic estimates based on incubated samples over the Posidonia oceanica meadow. Whereas the seagrass community was autotrophic, the excess organic carbon production therein could only balance the planktonic heterotrophy in shallow waters relative to the maximum depth of the bay ( 55 m). This generated a horizontal gradient from autotrophic or balanced communities in the shallow seagrass-covered areas, to strongly heterotrophic communities in deeper areas of the bay. It seems therefore that, on an annual scale in the whole bay, the organic matter production by the Posidonia oceanica may not be sufficient to fully compensate the heterotrophy of the planktonic compartment, which may require external organic carbon inputs, most likely from land

Evaluating the role of local mercury sources on spatial and temporal pollution trends in marine predators living in a changing arctic

peer reviewedThe consequences of a rapidly warming Arctic on environmental mercury (Hg) exposure in marine biota remains largely unknown. Stable carbon (C), nitrogen (N), sulphur (S) and Hg isotope ratios are increasingly used to harmonice and trace Hg sources, pathways and concentrations in marine top predators. Our objective was to identify Hg sources in marine Arctic predators at spatial and temporal scale and evaluate the consequences on Hg exposure over time. We measured THg concentrations, C, N, S, and Hg isotope ratios in muscle tissue of hooded Cystophora cristata and ringed seal Pusa hispida from East Greenland, collected between 1985 and 2019. We created multi-isotopic niches (standard ellipse areas, SEAs), after which we applied linear mixed models to relate temporal variation in Hg exposure and sources to environmental change (e.g. sea-ice, NAO). Hooded seals presented a larger SEA (mode, 95% CI: 0.93, 0.60 – 1.41) than ringed seals (mode, 95% CI: 0.22, 0.14 – 0.37). Ringed seals showed higher THg concentrations (Mean ± SD: 1.10 ± 0.48 µg g-1 dw) than hooded seals (0.88 ± 0.92 µg g-1 dw) on average. THg levels in hooded seal muscle decreased by 1.5% y-1, while no significant change was found for ringed seals. At spatial scale, habitat use (oceanic vs. coastal) was the most important driver of THg variability, with landfast ice-associated ringed seals being potentially influenced by enhanced coastal MeHg emission and accumulate higher THg levels. Attemporal scale, the shift in local marine biogeochemistry (represented by δ15N values) and prey biomass were the most important drivers of THg in ringed and hooded seals, respectively. The different Hg trends shown by the two species suggested how Hg sources are important drivers of bioaccumulation in Arctic seals, underling the necessity to reevalute their importance for the forecasting of future Hg trends in the Arctic Ocean