Biogeochemistry of dissolved free amino acids in marine sediments

Submitted in partial fulfillment of the requirements for the degree of Doctor of Philosophy at the Massachusetts Institute of Technology and the Woods Hole Oceanographic Institution August 1980Dissolved free amino acids (DFAA) were measured in interstitial water samples squeezed from sediments collected in a variety of depositional environments. These sediments were further characterized by measurements of total organic carbon, total nitrogen, dissolved organic carbon, total hydrolyzable amino acids, and pore water-dissolved remineralization products. Surface sediments from the oxygen minimum zone of the Peru Upwelling Region, which consisted of a filamentous bacterial mat, were sampled at three locations. DFAA concentrations within the mat ranged from 5 to 220 μM, with the highest concentrations found in the upper 4 cm at two stations on the landward and seaward edges of the zone, and lower concentrations at a station in the middle of the oxygen minimum zone. Within cores, lower concentrations were found at depths below the mat; and below 30 cm depth concentrations were between 0.7 and 3 μM. Two short cores of offshore sediments had concentrations between 14 and 40 μM (1400 m depth) and between 3 and 8 μM (5200 m). Glutamic acid was the predominant amino acid in nearly all surface sediments samples, making up 30 to 70 mole %. In sediments below 15 cm depth, β-aminoglutaric acid was often more abundant than glutamic acid and other amino acids were virtually absent. Glutamic acid, both from several analyses performed during this work and from data available in the literature is a major DFAA of bacterial pools, and bacteria are a likely source for the high concentrations seen in interstitial water samples. DFAA may be extracted from living cells by the squeezing process, or may be excreted by the bacteria under natural conditions. β-Aminoglutaric acid is s non-protein amino acid isomer of glutamic acid which has not been previously reported as a natural product. However, this work has shown it to be a constituent of the free amino acid pools of some bacteria at about 5 mole %. Its much larger relative abundance in sediments could stem from organisms which biosynthesize greater amounts than those analyzed, or from relatively slow biodegradation. Buzzards Bay, Massachusetts surface sediments (17 m water depth) also contained high DFAA concentrations, near; 50 μM, which decreased gradually with depth to about 5 μM at 30 cm. Glutamic acid and β-aminoglutaric acid were the major components, with β-aminoglutaric acid becoming relatively more abundant with depth in core. Repeated sampling of this station was carried out, and both the concentration and composition of DFAA in replicate samples was very similar. Sediments from the Pettaquamscutt River Estuary, Rhode Island (an anoxic basin), had low DFAA concentrations ranging from 2 to 6 μM. Glutamic and β-aminoglutaric acids made up 30 to 50 % of the total. Three cores of Gulf of Maine basin sediments had DFAA concentrations and compositions which were similar to each other and to Buzzards Bay sediments, except that glycine was a major constituent of some of the samples. Its distribution was irregular over the less than 30 cm depth intervals sampled. Glycine is the major DFAA in the pools of many benthic invertebrates. Its presence in these cores is consistent with independent evidence that Gulf of Maine basin sediments are extensively bioturbated. Two cores of carbonate-rich sediments from the continental rise to the east of the Gulf of Maine and from the Bermuda Rise had surface sediment DFAA concentrations of 33 and 0.9 μM, respectively. Despite the large difference in concentration, compositions were very similar, with glycine and glutamic acid the major constituents. The very low concentrations in the Bermuda Rise sediments may be related to very low metabolizable organic carbon concentrations. Two nonprotein amino acids, γ-aminobutyric acid and β-alanine, were major constituents of the total hydrolyzable amino acids in the Bermuda Rise sediments. Biological processes, specifically microbial, appear to be responsible for the major features of DFAA concentration and composition in the sediments studied. The concentrations of DFAA measured could be of significance to the nutrition of benthic organisms via transepidermal uptake or to the formation of humic substances in sediments, if these levels are found outside cells . However, as a sink for DFAA in sediments, the latter two processes are slow relative to microbial uptake.Financial support was provided by the Woods Hole Oceanographic Institution Education Office, the Paul M. Fye Fellowship, ONR Contract N00014-79-C-0071, and NSF Grant No. OCE 79-08665. Travel funds to Peru were provided by NSF Grant No. OCE 77-26180

BERING SEA ICE DYNAMICS AND PRIMARY PRODUCTION (17th Symposium on Polar Biology)

Sea ice communities in multi-year ice can accumulate a high algal biomass and develop a complex food web, and most higher trophic level biota of the regions north of 70 to 80° N depend on this for food. Further to the south, even within the seasonal sea ice zone, processes associated with the sea ice influence the biological regimes in important ways. For example, the biological spring is advanced on the order of weeks in the presence of sea ice, due to the development of populations of ice algae and subsequently, as the ice melts, the generation of an early spring bloom. In this paper, the influence of ice on the primary production regimes of arctic seas is discussed, with particular emphasis on the seasonal sea ice zone. Specific examples from recent work on the Berine Sea are included

Distributions of Nutrients, Dissolved Organic Carbon and Carbohydrates In the Western Arctic Ocean

Seawater samples were collected from stations along a transect across the shelf basin interface in the western Arctic Ocean during September 2002, and analyzed for nutrients, dissolved organic carbon (DOC), and total dissolved carbohydrate (TDCHO) constituents, including monosaccharides (MCHO) and polysaccharides (PCHO). Nutrients (nitrate, ammonium, phosphate and dissolved silica) were depleted at the surface, especially nitrate. Their concentrations increased with increasing depth, with maxima centered at similar to 125 m depth within the halocline layer, then decreased with increasing depth below the maxima. Both ammonium and phosphate concentrations were elevated in shelf bottom waters, indicating a possible nutrient source from sediments, and in a plume that extended into the upper halocline waters offshore. Concentrations of DOC ranged from 45 to 85 mu M and had an inverse correlation with salinity, indicating that mixing is a control on DOC concentrations. Concentrations of TDCHO ranged from 2.5 to 19 mu M-C, comprising 13-20% of the bulk DOC. Higher DOC concentrations were found in the upper water column over the shelf along with higher TDCHO concentrations. Within the TDCHO pool, the concentrations of MCHO ranged from 0.4 to 8.6 mu M-C, comprising 20-50% of TDCHO, while PCHO concentrations ranged from 0.5 to 13.6 mu M-C, comprising 50-80% of the TDCHO. The MCHO/TDCHO ratio was low in the upper 25 in of the water column, followed by a high MCHO/TDCHO ratio between 25 and 100 m, and a low MCHO/TDCHO ratio again below 100 m. The high MCHO/TDCHO ratio within the halocline layer likely resulted from particle decomposition and associated release of MCHO, whereas the low MCHO/TDCHO (or high PCHO/TDCHO) ratio below the halocline layer could have resulted from slow decomposition and additional particulate CHO sources. (c) 2006 Elsevier Ltd. All rights reserved