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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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TL;DR: In this paper, the authors presented an almost 3 year long time series of shell fluxes and oxygen isotopes of left-coiling Neogloboquadrina pachyderma and Turborotalita quinqueloba from sediment traps moored in the deep central Irminger Sea.
Abstract: [1] We present an almost 3 year long time series of shell fluxes and oxygen isotopes of left-coiling Neogloboquadrina pachyderma and Turborotalita quinqueloba from sediment traps moored in the deep central Irminger Sea. We determined their response to the seasonal change from a deeply mixed water column with occasional deep convection in winter to a thermally stratified water column with a surface mixed layer (SML) of around 50 m in summer. Both species display very low fluxes during winter with a remnant summer population holding out until replaced by a vital population that seeds the subsequent blooms. This annual population overturning is marked by a 0.7‰ increase in δ18O in both species. The shell flux of N. pachyderma peaks during the spring bloom and in late summer, when stratification is close to its minimum and maximum, respectively. Both export periods contribute about equally and account for >95% of the total annual flux. Shell fluxes of T. quinqueloba show only a single broad pulse in summer, thus following the seasonal stratification cycle. The δ18O of N. pachyderma reflects temperatures just below the base of the seasonal SML without offset from isotopic equilibrium. The δ18O pattern of T. quinqueloba shows a nearly identical amplitude and correlates highly with the δ18O of N. pachyderma. Therefore T. quinqueloba also reflects temperature near the base of the SML but with a positive offset from isotopic equilibrium. These offsets contrast with observations elsewhere and suggest a variable offset from equilibrium calcification for both species. In the Irminger Sea the species consistently show a contrast in their flux timings. Their flux-weighted Δδ18O will thus dominantly be determined by seasonal temperature differences at the base of the SML rather than by differences in their depth habitat. Consequently, their sedimentary Δδ18O may be used to infer the seasonal contrast in temperature at the base of the SML.
189 citations
01 Jan 1973
TL;DR: In the Pacific Ocean, the maximum concentrations of chlorophyll occur below the surface, typically in a narrow layer near or below the depth of penetration of 10/0 of the surface light as discussed by the authors.
Abstract: Data collected on several expeditions through the temperate and tropical Pacific Ocean show that during most of the year the maximum concentrations of chlorophyll occur below the surface, typically in a narrow layer near or below the depth of penetration of 10/0 of the surface light. The layer appears to be continuous across most of the Pacific although the depth and chlorophyll concentration vary regionally. The depth of the layer is more closely related to the depth of the nitrite maximum and to the position of the nutricline than to either light or density regimes. Productivity within the layer is low but positive, and contributes substantially to the total production of the water column. The maximum layer may be a seasonal phenomenon developing in the summer after the stabilization of the water column and mixing to the surface during the winter. Year to year fluctuations of depth and concentration of chlorophyll within the maximum layer may be related to large-scale meteorological fluctuations. Doty and Capurro (1961) have tabulated the position, date, depth, and values of chlorophyll and productivity in the world's oceans. There are several thousands of these measurements in the Pacific. Most are in the Northern Hemi sphere, and most are near land masses or is lands (e.g., Hawaii, Luzon, Hokkaido, New Cal edonia, New Zealand), along the equator, or north of lat 40 0
189 citations
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TL;DR: In this article, the authors characterized the major carbon pathways in a humic lake, determined carbon pool sizes and main pathways by long-term tracer studies in enclosures, and found that dissolved organic carbon (DOC) was by far the largest pool and constituted 80-85% of total carbon.
Abstract: To characterize the major carbon pathways in a humic lake, we determined carbon pool sizes and main pathways by long-term tracer studies in enclosures. Dissolved organic carbon (DOC) was by far the largest pool and constituted 80–85% of total carbon. In the water column particulate organic carbon was partitioned between detritus, zooplankton, bacteria, and phytoplankton at ratios of 22 : 4 : 3 : 1. Phytoplankton and bacterioplankton production averaged 24 and 32 µg C liter−1 d−1, while crustacean zooplankton production was very low (<5 µg C liter−1 d−1) during the experiment. Total pelagic community respiration was high, giving a net CO2 flux to the atmosphere of 44 µg C liter−1 d−1, while losses by sedimentation were negligible.
Most of the particulate carbon available for zooplankton was highly recycled detritus of low nutritional value. The loop of ingestion and defecation of detrital particles was a major carbon pathway, giving detrital particles a turnover rate of 0.39 d−1. Detritus was found to support 46–82% of body carbon in the surveyed species, with Acanthodiaptomus as the upper extreme. Bacterial carbon accounted for 11–42% of body carbon and phytoplankton for 6–19% in the surveyed species.
189 citations
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TL;DR: The results of several studies on P dynamics in wetlands and stream sediments in the Lake Okeechobee Basin with primary focus on P interaction with soil/sediment-water column and vegetation were summarized in this paper.
189 citations
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TL;DR: In this paper, high-resolution records of opal, carbonate, and terrigenous fluxes have been obtained from a high-sedimentation rate core (MD84-527: 43°50′S; 51°19;′E; 3269 m) by normalization to 230Th.
Abstract: High-resolution records of opal, carbonate, and terrigenous fluxes have been obtained from a high-sedimentation rate core (MD84-527: 43°50′S; 51°19;′E; 3269 m) by normalization to 230Th. This method estimates paleofluxes to the seafloor on a point-by-point basis and distinguishes changes in sediment accumulation due to variations in vertical rain rates from those due to changes in syndepositional sediment redistribution by bottom currents. We also measured sediment δ15N to evaluate the changes in nitrate utilization in the overlying surface waters associated with paleoflux variations. Our results show that opal accumulation rates on the seafloor during the Holocene and stage 3, based on 14C dating, were respectively tenfold and fivefold higher than the vertical rain rates, At this particular location, changes in opal accumulation on the seafloor appear to be mainly controlled by sediment redistribution by bottom currents rather than variations in opal fluxes from the overlying water column. Correction for syndepositional sediment redistribution and the improved time resolution that can be achieved by normalization to 230Th disclose important variations in opal rain rates. We found relatively high but variable opal paleoflux during stage 3, with two maxima centered at 36 and 30 kyr B.P., low opal paleoflux during stage 2 and deglaciation and a pronounced maximum during the early Holocene, We interpret this record as reflecting variations in opal production rates associated with climate-induced latitudinal migration of the southern ocean frontal system. Sediments deposited during periods of high opal paleoflux also have high authigenic U concentrations, suggesting more reducing conditions in the sediment, and high Pa-231/Th-230 ratios, suggesting increased scavenging from the water column. Sediment δ15N is circa 1.5 per mil higher during isotopic stage 2 and deglaciation. The low opal rain rates recorded during that period appear to have been associated with increased nitrate depletion. This suggests that opal paleofluxes do not simply reflect latitudinal migration of the frontal system but also changes in the structure of the upper water column. Increased stratification during isotopic stage 2 and deglaciation could have been produced by a meltwater lid, leading to lower nitrate supply rates to surface waters.
188 citations