Oxygen Depletion in Coastal Waters and the Open Ocean

Organic- and sulfide-rich sediments have formed in oxygen-depleted environments throughout Earth’s history. The fact that they are generally enriched in redox-sensitive elements reflects the sedimentary environment at the time of deposition. Although the modern ocean is well oxidized, oxygen depletion occurs in certain areas such as restricted basins and high-productivity zones. We measured bulk chemical compositions (major and trace elements, total organic carbon, and total sulfur) of organic- and sulfide-rich sediments collected from eight areas having oxygen-depleted water to discuss relationships between geochemical features and sedimentary environments. Major elemental compositions generally show mixtures of terrigenous detritus and biogenic carbonate. Some redox-sensitive elements might be controlled by organic matter content, whereas others could be contained in sulfide minerals in sediments. In particular, Mo and U show a characteristic trend; areas with higher Mo and U—at least partially owing to a depositional process called the “particulate shuttle”—generally correspond to regions influenced by the open ocean. In contrast, areas with lower Mo and U are more restricted marine environments. This suggests that the degree of Mo and U enrichment reflects the geography in terms of proximity to the open ocean, or the degree of the supply of these elements from the open ocean.

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Carbon dynamics and CO<sub>2</sub> air-sea exchanges in the eutrophied coastal waters of the Southern Bight of the North Sea: a modelling study

Biogeosciences ◽

10.5194/bg-1-147-2004 ◽

2004 ◽

Vol 1 (2) ◽

pp. 147-157 ◽

Cited By ~ 20

Author(s):

N. Gypens ◽

C. Lancelot ◽

A. V. Borges

Keyword(s):

Surface Water ◽

Coastal Zone ◽

North Sea ◽

Coastal Waters ◽

Co2 Flux ◽

Open Ocean ◽

Atmospheric Co2 ◽

Southern Bight ◽

The North ◽

The North Sea

Abstract. A description of the carbonate system has been incorporated in the MIRO biogeochemical model to investigate the contribution of diatom and Phaeocystis blooms to the seasonal dynamics of air-sea CO2 exchanges in the Eastern Channel and Southern Bight of the North Sea, with focus on the eutrophied Belgian coastal waters. For this application, the model was implemented in a simplified three-box representation of the hydrodynamics with the open ocean boundary box ‘Western English Channel’ (WCH) and the ‘French Coastal Zone’ (FCZ) and ‘Belgian Coastal Zone’ (BCZ) boxes receiving carbon and nutrients from the rivers Seine and Scheldt, respectively. Results were obtained by running the model for the 1996–1999 period. The simulated partial pressures of CO2 (pCO2) were successfully compared with data recorded over the same period in the central BCZ at station 330 (51°26.05′ N; 002°48.50′ E). Budget calculations based on model simulations of carbon flow rates indicated for BCZ a low annual sink of atmospheric CO2 (−0.17 mol C m-2 y-1). On the opposite, surface water pCO2 in WCH was estimated to be at annual equilibrium with respect to atmospheric CO2. The relative contribution of biological, chemical and physical processes to the modelled seasonal variability of pCO2 in BCZ was further explored by running model scenarios with separate closures of biological activities and/or river inputs of carbon. The suppression of biological processes reversed direction of the CO2 flux in BCZ that became, on an annual scale, a significant source for atmospheric CO2 (+0.53 mol C m-2 y-1). Overall biological activity had a stronger influence on the modelled seasonal cycle of pCO2 than temperature. Especially Phaeocystis colonies which growth in spring were associated with an important sink of atmospheric CO2 that counteracted the temperature-driven increase of pCO2 at this period of the year. However, river inputs of organic and inorganic carbon were shown to increase the surface water pCO2 and hence the emission of CO2 to the atmosphere. Same calculations conducted in WCH, showed that temperature was the main factor controlling the seasonal pCO2 cycle in these open ocean waters. The effect of interannual variations of fresh water discharge (and related nutrient and carbon inputs), temperature and wind speed was further explored by running scenarios with forcing typical of two contrasted years (1996 and 1999). Based on these simulations, the model predicts significant variations in the intensity and direction of the annual air-sea CO2 flux.

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Dead Zones

10.1093/oso/9780197520376.001.0001 ◽

2021 ◽

Cited By ~ 1

Author(s):

David L. Kirchman

Keyword(s):

Cover Crops ◽

Precision Agriculture ◽

Coastal Waters ◽

Harmful Algal Blooms ◽

Algal Blooms ◽

Biological Diversity ◽

Oxygen Depletion ◽

Waterborne Diseases ◽

Buffer Zones ◽

Dead Zones

This book explores the many rivers, lakes, and oceans that are losing oxygen. Aquatic habitats with little dissolved oxygen are called dead zones because nothing can live there except some microbes. The number and size of dead zones are increasing worldwide. The book shows that oxygen loss causes fish kills, devastates bottom-dwelling biota, reduces biological diversity, and rearranges aquatic food webs. In the 19th century in rich countries and in poor regions today, dead zones are accompanied by waterborne diseases that kill thousands of people. The open oceans are losing oxygen because of climate change, whereas dead zones in coastal waters and seas are caused by excessive nutrients, which promote excessive growth of algae and eventually oxygen depletion. Work by Gene Turner and Nancy Rabalais demonstrated that nutrients in the Gulf of Mexico come from fertilizers used in the US Midwest, home to the most productive cropland in the world. Agriculture is also the biggest source of nutrients fuelling dead zones in the Baltic Sea and other coastal waters. Today, fertilizers contaminate drinking water and kick-start harmful algal blooms in local lakes and reservoirs. Nutrient pollution in some regions has declined because of buffer zones, cover crops, and precision agriculture, but more needs to be done. The book concludes by arguing that each of us can do our part by changing our diet; eating less, especially eating less red meat, would improve our health and the health of the environment. A better diet could reduce the amount of greenhouse gas emitted by agriculture and shrink dead zones worldwide.

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Mg/Ca and Mn/Ca ratios in benthic foraminifera: the potential to reconstruct past variations in temperature and hypoxia in shelf regions

Biogeosciences ◽

10.5194/bg-10-5125-2013 ◽

2013 ◽

Vol 10 (7) ◽

pp. 5125-5138 ◽

Cited By ~ 33

Author(s):

J. Groeneveld ◽

H. L. Filipsson

Keyword(s):

Dissolved Oxygen ◽

Trace Metal ◽

Benthic Foraminifera ◽

Bottom Water ◽

Oxygen Depletion ◽

Open Ocean ◽

Low Oxygen ◽

Saturation State ◽

Bottom Water Temperature ◽

Fish And Shellfish

Abstract. Shelf and coastal regions are exceptionally important for many countries as they provide the main habitat for many economically important fish and shellfish species. With ongoing climate change and human-induced eutrophication the shelf regions are especially affected, resulting in increased temperatures and stratification as well as oxygen depletion of the bottom waters. In order to be able to predict the magnitude of these changes in the future, it is necessary to study how they varied in the past. Commonly used foraminiferal climate and environmental proxies, e.g., stable isotopes and trace metal/Ca ratios, that are applied in open-ocean settings are not necessarily applicable in shelf regions, either as faunas are significantly different or as conditions can change much faster compared to the open ocean. In this study we explore the use of Mg/Ca as paleothermometer and Mn/Ca as a potential proxy for changing dissolved oxygen conditions in bottom water on the benthic foraminifera Bulimina marginata and Globobulimina turgida. Living specimens were collected from the Skagerrak and the Gullmar Fjord (SW Sweden); the latter is hypoxic for several months a year. As the specimens were alive when collected, we assume it unlikely that any diagenetic coatings have already significantly affected the trace metal/Ca ratios. The Mg/Ca ratios are similar to previously published values but display much larger variation than would be expected from the annual temperature change of less than 2 °C. An additional impact of the difference in the calcite saturation state between the Skagerrak and the Gullmar Fjord could explain the results. Mn/Ca ratios from G. turgida can potentially be related to variations in dissolved oxygen of the habitat where the foraminifera calcify. Samples from the Skagerrak display increased Mn/Ca in specimens that lived deeper in the sediment than those that lived near the surface. G. turgida samples from the low-oxygen Gullmar Fjord showed significantly increased Mn/Ca, being highest when bottom water dissolved oxygen was at a minimum. Our study suggests that trace metal/Ca ratios in benthic foraminifera from shelf regions have the potential to record past variations in bottom water temperature and dissolved oxygen concentrations, but an additional impact of the inorganic carbonate chemistry cannot be excluded.

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Metal speciation from stream to open ocean: modelling v. measurement

Environmental Chemistry ◽

10.1071/en15111 ◽

2016 ◽

Vol 13 (3) ◽

pp. 464 ◽

Cited By ~ 11

Author(s):

Edward Tipping ◽

Stephen Lofts ◽

Anthony Stockdale

Keyword(s):

Coastal Waters ◽

Natural Waters ◽

Chemical Speciation ◽

Metal Speciation ◽

Open Ocean ◽

Large Set ◽

Data Set ◽

Fresh Waters ◽

Speciation Model ◽

Model Predictions

Environmental contextThe chemical speciation of metals strongly influences their transport, fate and bioavailability in natural waters. Analytical measurement and modelling both play important roles in understanding speciation, while modelling is also needed for prediction. Here, we analyse a large set of data for fresh waters, estuarine and coastal waters, and open ocean water, to examine how well measurements and modelling predictions agree. AbstractWe compiled a data set of ~2000 published metal speciation measurements made on samples of fresh waters, estuarine and coastal waters, and open ocean waters. For each sample, we applied the chemical speciation model WHAM7 to calculate the equilibrium free metal ion concentrations, [M] (molL–1), amounts of metal bound by dissolved organic matter (DOM), ν (molg–1), and their ratio ν/[M] (L g–1), which is a kind of ‘local’ partition coefficient. Comparison of the measured and predicted speciation variables for the whole data set showed that agreements are best for fresh waters, followed by estuarine and coastal waters, then open-ocean waters. Predicted values of ν/[M], averaged over all results for each metal, closely follow the trend in average measured values, confirming that metal reactivity, and consequent complexation by DOM, in natural waters accord with the expectations of the speciation model. Comparison of model predictions with measurements by different analytical techniques suggests that competitive ligand–stripping voltammetry methods overestimate metal complexation by DOM, and therefore underestimate [M]. When measurements by other methods are compared with predictions, for all metals, reasonable agreement with little bias is obtained at values of ν>10–6molg–1 DOM, but at lower values of ν, the model predictions of [M] are mostly higher than the measured values, and the predictions of ν and ν/[M] are mostly lower. Research is needed to establish whether this reflects analytical error or the failure of the model to represent natural high-affinity ligands.

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Biological production of methyl bromide in the coastal waters of the North Sea and open ocean of the northeast Atlantic

Marine Chemistry ◽

10.1016/s0304-4203(98)00077-2 ◽

1999 ◽

Vol 64 (4) ◽

pp. 267-285 ◽

Cited By ~ 36

Author(s):

J.M Baker ◽

C.E Reeves ◽

P.D Nightingale ◽

S.A Penkett ◽

S.W Gibb ◽

...

Keyword(s):

North Sea ◽

Methyl Bromide ◽

Coastal Waters ◽

Open Ocean ◽

Biological Production ◽

Northeast Atlantic ◽

The North ◽

The North Sea

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Fatty Acids Derived from Lipids of Marine Origin

Journal of the Fisheries Research Board of Canada ◽

10.1139/f65-100 ◽

1965 ◽

Vol 22 (5) ◽

pp. 1107-1122 ◽

Cited By ~ 41

Author(s):

P. M. Williams

Keyword(s):

Fatty Acids ◽

Fatty Acid ◽

Coastal Waters ◽

Acid Content ◽

Surface Sediments ◽

Sea Water ◽

Fatty Acid Content ◽

Dry Weight ◽

Open Ocean ◽

Marine Origin

Fatty Acids in sea water were found in concentrations of 1–9 μg/litre and 1–30 μg/litre for the dissolved and particulate fractions, respectively. Little variations were observed with depth or along a profile from coastal waters out into the open ocean. The total dissolved fatty acid concentrations were 10 to 100 times lower than had been previously reported. The fatty acid content of surface sediments varied from 13 to 67 μg/g dry weight of sediment.Six species of marine phytoplanktonic algae, two zooplankton samples, and liver extracts from hake and whiting were analyzed for their fatty acid content. The algae showed individual patterns in the spectrum of fatty acids present. The zooplankton samples were similar to the hake and whiting liver extracts with respect to the ratios of palmitic to palmitoleic and stearic to oleic acids.

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