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Water column

About: Water column is a research topic. Over the lifetime, 13706 publications have been published within this topic receiving 496626 citations.


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Journal ArticleDOI
TL;DR: The flux of diatom valves and radiolarian shells obtained during short-term and annual sediment trap experiments at seven localities in the Atlantic sector of the Antarctic Ocean (in the Drake Passage, Bransfield Strait, Powell Basin, NW and SE Weddell Sea and the Polar Front north of Bouvet Island) is summarized and discussed in this article.

153 citations

Journal ArticleDOI
TL;DR: In this paper, the authors obtained seasonal or longer-term data sets on the rates of production, vertical transport, remineralization and burial of particulate organic carbon (POC) and biogenic silica (BSiO2) in the Southern Ocean at 170°W between 55°S and 68°S.
Abstract: During the 1996–1998 Antarctic Environment and Southern Ocean Process Study (AESOPS), a component of US JGOFS, we obtained seasonal or longer-term data sets on the rates of production, vertical transport, remineralization and burial of particulate organic carbon (POC) and biogenic silica (BSiO2) in the Southern Ocean at 170°W between 55°S and 68°S. The AESOPS data records enable us to construct vertical C and Si budgets for the water column and upper sediments, with all estimates derived from direct measurement of the relevant fluxes. We constructed annual C and Si budgets for each of four ecologically distinct zonal bands within the system. For both POC and BSiO2 the greatest annual delivery to the sea floor (∼200 and 1400 mmol m−2 yr−1, respectively) and burial (∼6 and 160 mmol m−2 yr−1, respectively) were observed in the southern Antarctic Circumpolar Current (ACC) between 61.5°S and 65.5°S. That pattern is consistent with our observation that a diatom bloom propagated southward through the southern ACC during the spring and summer of 1997–1998, following the receding ice edge, and that this bloom was the main source of both POC and BSiO2 in the system on an annual basis. In the other zones the annual fluxes of POC and BSiO2 to the sea floor ranged from 19% to 67% of those in the zone traversed by the summer diatom bloom. The higher benthic fluxes of both POC and BSiO2 in the southern ACC imply that blooms similar to the one we observed in 1997–1998 occur commonly in the southern ACC, and that their high-productivity signature is transmitted to the sea floor. The data show preferential preservation of BSiO2 over POC throughout the water column and upper seabed. In the four zonal bands we consider, BSiO2 and POC are produced in mole ratios of 0.1–0.4, exported from the upper 100 m in ratios of 0.2–0.6, arrive at 1000 m in ratios of 1.5–4.5, reach the sea floor in ratios of 2.2–7.6, and are buried in ratios of 11.6–28. Despite the preferential preservation of BSiO2, accumulation of opal-rich sediments beneath the ACC does not result from unusually efficient preservation of siliceous material. The estimated BSiO2 preservation efficiency (burial-production) ranges from 1.2% to 5.5%, indistinguishable from the global average of 3%. Instead, opal-rich sediment accumulation in this region reflects very high annual rates of BSiO2 production in surface waters, along with very low accumulation rates of other sedimentary components (e.g., CaCO3 and detrital material). The observed high ratios of BSiO2 production to POC production in surface waters are consistent with the known tendency for the Si/C ratio of diatoms to increase when [Fe] is low. If greater Fe availability during the last glacial maximum permitted diatoms in the Southern Ocean to grow with lower, more normal Si/C ratios, export of diatom-produced POC could have occurred at 2–3 times its present rate. A corresponding increase in opal export or opal sediment accumulation is unlikely because silicic acid is almost totally depleted north of 65°S under present conditions. Thus, even large increases in POC production and export during glacial periods would not be reflected in the opal accumulation record.

153 citations

Journal ArticleDOI
TL;DR: Dissolved DNA and a series of microbial biomass and activity parameters were measured in offshore, coastal, estuanne and coral reef environments of the southeast Gulf of Mexico as discussed by the authors, and the results were discussed in terms of the potential for transformation by dissolved DNA.
Abstract: Dissolved DNA and a series of microbial biomass and activity parameters were measured in offshore, coastal, estuanne and coral reef environments of the southeast Gulf of Mexico. Oceanic concentrations of dissolved DNA ranged from 0.2 to 19 vg 1-' and decreased as a function of distance from shore and depth in the water column. Dissolved DNA concentrations were greater than half the particulate DNA content in offshore environments (Z = 63 + 45 O/O), but were a smaller percentage of particulate DNA in nearshore and estuarine environments (Z = 35 f 21 %). Dissolved DNA correlated better with bacterial parameters (i.e. bacterial direct counts, particulate DNA and thymidine incorporation) than with phytoplankton parameters (chlorophyll a, primary productivity). The molecular weight (MW) of dissolved DNA (determined by agarose gel electrophoresis) ranged from 0.12 kilobase pairs (kb; 7.75 X 104 daltons) to 35.2 kb (2.32 X 10' daltons) for estuarine samples, while an oligotrophic environment contained smaller MW DNA (range 0.24 to 14.27 kb). DNA fragments in this size range are sufficient to contain gene sequences. These results are discussed in terms of the potential for transformation by dissolved DNA.

153 citations

Journal ArticleDOI
01 Mar 2001-Boreas
TL;DR: Foraminiferal assemblages were studied in northern Barents Sea core ASV 880 along with oxygen and carbon isotope measurements in planktonic (N. pachyderma sin.) and benthic (E clavatum) species as mentioned in this paper.
Abstract: Foraminiferal assemblages were studied in northern Barents Sea core ASV 880 along with oxygen and carbon isotope measurements in planktonic (N. pachyderma sin.) and benthic (E clavatum) species. AMS C-14 measurements performed on molluscs Yoldiella spp. show that this core provides a detailed and undisturbed record of Holocene climatic changes over the last 10000 calendar years. Surface and deep waters were very cold (<0°C) at the beginning of the Holocene. C. reniforme dominated the highly diverse benthic foraminiferal assemblage. From 10 to 7.8 cal. ka BP, a warming trend culminated in a temperature optimum, which developed between 7.8 and 6.8 cal. ka BP. During this optimum, the input of Atlantic water to the Barents Sea reached its maximum. The Atlantic water mass invaded the whole Franz Victoria Trough and was present from subsurface to the bottom. No bottom water, which would form through rejection of brine during winter, was present at the core depth (388 m). The water stratification was therefore greatly reduced as compared to the present. An increase in percentage of I. helenae/norcrossi points to long seasonal ice-free conditions. The temperature optimum ended rather abruptly, with the return of cold polar waters into the trough within a few centuries. This was accompanied by a dramatic reduction of the abundance of C. reniforme. During the upper Holocene, the more opportunistic species E. clavatum became progressively dominant and the water column was more stratified. Deep water in Franz Victoria Trough contained a significant amount of cold Barents Sea bottom water as it does today, while subsurface water warmed progressively until about 3.7 cal. ka BP and reached temperatures similar to those of today. These long-term climatic changes were cut by several cold events of short duration, in particular one in the middle of the temperature optimum and another, which coincides most probably with the 8.2 ka BP cold event. Both long- and short-term climatic changes in the Barents Sea are associated with changes in the flow of Atlantic waters and the oceanic conveyor belt.

153 citations

Journal ArticleDOI
TL;DR: In this paper, the influence of biological and physical factors on DO dynamics in an estuarine ecosystem near Calvert Cliffs, Chesapeake Bay was examined for the first time.

153 citations


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Performance
Metrics
No. of papers in the topic in previous years
YearPapers
2023458
2022969
2021497
2020502
2019502
2018466