Characteristics, dynamics and significance of marine snow

The bubble mechanism for methane transport from the shallow sea bed to the surface: A review and sensitivity study

. Results from a study of surfactants in the sea-surface microlayer (SML) in different regions of the ocean (subtropical, temperate, polar) suggest that this interfacial layer between the ocean and atmosphere covers the ocean's surface to a significant extent. New, experimentally-derived threshold values at which primary production acts as a significant source of natural surfactants to the microlayer are coupled with a wind speed threshold at which the SML is presumed to be disrupted, and the results suggest that surfactant enrichment in the SML is greater in oligotrophic regions of the ocean than in more productive waters. Furthermore, surfactant enrichments persisted at wind speeds of up to 10 m s−1, without any observed depletion above 5 m s−1. This suggests that the SML is stable enough to exist even at the global average wind speed of 6.6 m s−1. Using our observations of the surfactant enrichments at various trophic levels and wind states, global maps of primary production and wind speed allow us to extrapolate the ocean's SML coverage . The maps indicate that wide regions of the Pacific and Atlantic Oceans between 30° N and 30° S may be more significantly covered with SML than north of 30° N and south of 30° S, where higher productivity (spring/summer blooms) and wind speeds exceeding 12 m s−1 may prevent extensive SML formation.

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Formation and global distribution of sea-surface microlayers

Organic chelators that are thought to be of recent biological origin control copper speciation in seawater. Previous studies have often resolved these copper binding ligands into two classes, class 1 ligands (conditional stability constants 10 12 ‐10 14 M 21 ) and class 2 ligands (conditional stability constants 10 9 ‐10 12 M 21 ). At present the sources and structures of these chelators are unknown. Previous work has shown that in response to copper toxicity, cultures of the marine cyanobacteria Synechococcus spp. produce a strong ligand, similar in binding strength to class 1 ligands. We extended this work by surveying a suite of copper-stressed marine eucaryotic phytoplankton for the production of copper binding ligands. Most eucaryotic species we studied did not produce ligands with the binding strength of class 1 ligands, but many produced class 2 ligands. A marine dinoflagellate Amphidinium carteraewas found to produce very strong ligands; however, the low abundance of dinoflagellates in the open ocean may mean that this source of class 1 ligands is more important in coastal waters. This survey shows that there are many biological sources of copper binding ligands, but that procaryotes such as cyanobacteria are more plausible sources of class 1 ligands in the open ocean than eucaryotes. There is now considerable evidence to suggest that the distribution and speciation of trace metals in the upper water column play an important role in the species composition and physiology of phytoplankton assemblages (Sunda 1994). The chemical speciation of trace metals is important because only certain forms of a given metal are biologically available. In the upper water column, speciation of many biologically active trace metals is controlled by complexation with strong organic ligands (Bruland et al. 1991 and references therein). Complexation of the metal by an organic ligand generally lowers biological availability because the free metal ions are the most biologically available forms (Sunda 1994; Campbell 1995). In addition, complexation may play an important role in the geochemical cycling of these elements in the upper ocean. For many elements, concentrations of these ligands are highest in the euphotic zone and decline to non-detectable levels in the deep waters (Bruland et al. 1991; Rue and Bruland 1995). This distribution suggests that the ligands are of recent biological origin and are not refractory compounds. However, their biological function, if any, is unknown. Complexation is particularly important for Cu, an essential micronutrient that is also toxic. Field studies in coastal

https://aslopubs.onlinelibrary.wiley.com/doi/pdf/10.4319/lo.2000.45.3.0619

Production of extracellular Cu complexing ligands by eucaryotic phytoplankton in response to Cu stress

This article reviews progress in the research of methyl mercury (MeHg) and nutrient interactions during the past two decades. Special emphasis is placed on the following three major areas: a) effects on kinetics, b) effects on toxicity, and c) possible mechanisms. Dietary information is not usually collected in most epidemiologic studies examining of the effects of MeHg exposure. However, inconsistency of the MeHg toxicity observed in different populations is commonly attributed to possible effects of dietary modulation. Even though the mechanisms of interaction have not been totally elucidated, research in nutritional toxicology has provided insights into the understanding of the effects of nutrients on MeHg toxicity. Some of this information can be readily incorporated into the risk assessment of MeHg in the diets of fish-eating populations. It is also clear that there is a need for more studies designed specifically to address the role of nutrition in the metabolism and detoxification of MeHg. It is also important to collect more detailed dietary information in future epidemiologic studies of MeHg exposure.

Boẑena Ćosović

Papers

Surfactant production by marine phytoplankton

Determination of surfactant activity and anionic detergents in seawater and sea surface microlayer in the Mediterranean

Interaction of cadmium and copper with surface-active organic matter and complexing ligands released by marine phytoplankton

Electrochemical estimation of the dominant type of surface active substances in seawater samples using o-nitrophenol as a probe

The adsorption and interaction of long-chain fatty acids and heavy metals at the mercury electrode/sodium chloride solution interface