126,076 research outputs found
Strong hydrographic controls on spatial and seasonal variability of dissolved organic carbon in the Chukchi Sea
No full textA detailed analysis of dissolved organic carbon (DOC) distribution in the Western Arctic Ocean was performed during the spring and summer of 2002 and the summer of 2003. DOC concentrations were compared between the three cruises and with previously reported Arctic work. Concentrations of DOC were highest in the surface water where they also showed the highest degree of variability spatially, seasonally, and annually. Over the Canada Basin, DOC concentrations in the main water masses were: (1) surface layer (71±4 ?M, ranging from 50 to 90 ?M); (2) Bering Sea winter water (66±2 ?M, ranging from 58 to 75 ?M); (3) halocline layer (63±3 ?M, ranging from 59 to 68 ?M), (4) Atlantic layer (53±2 ?M, ranging from 48 to 57 ?M), and (5) deep Arctic layer (47±1 ?M, ranging from 45 to 50 ?M). In the upper 200 m, DOC concentrations were correlated with salinity, with higher DOC concentrations present in less-saline waters. This correlation indicates the strong influence that fluvial input from the Mackenzie and Yukon Rivers had on the DOC system in the upper layer of the Chukchi Sea and Bering Strait. Over the deep basin, there appeared to be a relationship between DOC in the upper 10 m and the degree of sea-ice melt water present. We found that sea-ice melt water dilutes the DOC signal in the surface waters, which is contrary to studies conducted in the central Arctic Ocean
The role of ocean acidification in systemic carbonate mineral suppression in the Bering Sea
No full textOcean acidification driven by absorption of anthropogenic carbon dioxide (CO2) from the atmosphere is now recognized as a systemic, global process that could threaten diverse marine ecosystems and a number of commercially important species. The change in calcium carbonate (CaCO3) mineral saturation states (?) brought on by the reduction of seawater pH is most pronounced in high latitude regions where unique biogeochemical processes create an environment more susceptible to the suppression of ? values for aragonite and calcite, which are critical to shell building organisms. New observations from the eastern Bering Sea shelf show that remineralization of organic matter exported from surface waters rapidly increases bottom water CO2 concentrations over the shelf in summer and fall, suppressing ? values. The removal of CO2 from surface waters by high rates of phytoplankton primary production increases ? values between spring and summer, but these increases are partly counteracted by mixing with sea ice melt water and terrestrial river runoff that have low ? values. While these environmental processes play an important role in creating seasonally low saturation states, ocean uptake of anthropogenic CO2 has shifted ? values for aragonite to below the saturation horizon in broad regions across the shelf for at least several months each year. Furthermore, we also report that calcite became undersaturated in September of 2009 in the bottom waters over the shelf. The reduction in CaCO3 mineral saturation states could have profound implications for several keystone calcifying species in the Bering Sea, particularly the commercially important crab fisheries
Ocean acidification and biologically induced seasonality of carbonate mineral saturation states in the western Arctic Ocean
No full textCalcium carbonate (CaCO3) mineral saturation states for aragonite (?aragonite) and calcite (?calcite) are calculated for waters of the Chukchi Sea shelf and Canada Basin of the western Arctic Ocean during the Shelf-Basin Interactions project from 2002 to 2004. On the Chukchi Sea shelf, a strong seasonality and vertical differentiation of aragonite and calcite saturation states was observed. During the summertime sea ice retreat period, high rates of phytoplankton primary production and net community production act to increase the ?aragonite and ?calcite of surface waters, while subsurface waters become undersaturated with respect to aragonite due primarily to remineralization of organic matter to CO2. This seasonal “phytoplankton-carbonate saturation state” interaction induces strong undersaturation of aragonite (?aragonite = <0.7–1) at ?40–150 m depth in the northern Chukchi Sea and in the Canada Basin within upper halocline waters at ?100–200 m depth. Patches of aragonite undersaturated surface water were also found in the Canada Basin resulting from significant sea ice melt contributions (>10%). The seasonal aragonite undersaturation of waters observed on the Chukchi Sea shelf is likely a recent phenomenon that results from the uptake of anthropogenic CO2 and subsequent ocean acidification, with seasonality of saturation states superimposed by biological processes. These undersaturated waters are potentially highly corrosive to calcifying benthic fauna (e.g., bivalves and echinoderms) found on the shelf, with implications for the food sources of large benthic feeding mammals (e.g., walrus, gray whales, and bearded seals). The benthic ecosystem of the Chukchi Sea (and other Arctic Ocean shelves) is thus potentially vulnerable to future ocean acidification and suppression of CaCO3 saturation states
Coupling primary production and terrestrial runoff to ocean acidification and carbonate mineral suppression in the eastern Bering Sea
No full textWater column pH and carbonate mineral saturation states were calculated from dissolved inorganic carbon (DIC) and total alkalinity data collected over the eastern Bering Sea shelf in the spring and summer of 2008. The saturation states (?) of the two most important carbonate minerals, calcite (?calcite) and aragonite (?aragonite) were strongly coupled to terrestrial runoff from the Yukon and Kuskokwim rivers, primary production in the surface waters, and remineralization of organic matter at depth over the shelf. In spring, before ice melt occurred, pH over the shelf was largely confined to a range of 7.9–8.1 and ?calcite and ?aragonite ranged from 1.5 to 3.0 and 0.8 to 2.0, respectively. At the stations closest to river outflows, aragonite was undersaturated in the water column from the surface to the bottom. During the summer sea ice retreat, high rates of primary production consumed DIC in the mixed layer, which increased pH and ?calcite and ?aragonite. However, ?calcite and ?aragonite decreased by ?0.3 in the bottom waters over the middle and outer shelf. Over the northern shelf, where export production is highest, ?aragonite decreased by ?0.35 and became highly undersaturated. The observed suppression and undersaturation of ?calcite and ?aragonite in the eastern Bering Sea are correlated with anthropogenic carbon dioxide uptake into the ocean and will likely be exacerbated under business-as-usual emission scenarios. Therefore, ocean acidification could threaten some benthic and pelagic calcifying organisms across the Bering Sea shelf in the coming decades
Hydrographic controls on net community production and total organic carbon distributions in the eastern Bering Sea
No full textIn order to assess spatial and temporal variability of net community production (NCP) in shelf areas of the eastern Bering Sea, seawater samples for dissolved inorganic carbon (DIC) and total organic carbon (TOC) were collected during BEST-BSIERP cruises in the spring, summer, and fall of 2009 and compared to prior measurements made in 2008. DIC and TOC data were used to estimate seasonal changes in rates of NCP and the balance of net autotrophy versus heterotrophy in different shelf areas. In 2009, springtime surface layer DIC concentrations were generally uniform across the shelf and averaged ?2100 ?mol kg?1, although concentrations in northern shelf areas (under sea-ice cover) were slightly higher (?2130 ?mol kg?1). Subsequently, surface layer DIC (?1950 ?mol kg?1) decreased significantly by summertime with the largest drawdown of DIC observed in the Middle Domain between 57° and 61°N. In this area, high NCP rates of up to 92 mmol C m?2 d?1 were observed and were higher than those reported in 2008. Comparing 2008 and 2009, the shelfwide average drawdown of DIC in the upper 30 m between spring and summer was greater by ?16 ?mol kg?1. In both spring and summer of 2008 and 2009, concentrations of TOC generally decreased from the coast. TOC concentrations were tightly coupled to salinity, particularly in spring, and largely influenced by the discharge of the Yukon and Kuskokwim Rivers. TOC accumulation between spring and summer was relatively small. In nearshore regions of the shelf, negative rates of NCP observed in 2009 were indicative of net heterotrophy with remineralization of labile organic carbon from rivers likely contributing to the observed net respiration signal in this region. In contrast, net heterotrophy was not observed in 2008, when river discharge rates were 30% lower (likely with lower river transport of TOC). While 2009 rates of production were higher outside the coastal domain than those observed in 2008, integrated annual production over the shelf was fairly comparable between the two years (2008: 103 Tg C yr?1; 2009: 97.2 Tg C yr?1). DOC accumulation in the surface layer was also equivalent between the two years (?12 ?mol kg?1), and in both years shelfwide export production was estimated to be ?75% of total NCP
Eddy transport of organic carbon and nutrients from the Chukchi Shelf : impact on the upper halocline of the western Arctic Ocean
No full textAuthor Posting. © American Geophysical Union, 2007. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Journal of Geophysical Research 112 (2007): C05011, doi:10.1029/2006JC003899.In September 2004 a detailed physical and chemical survey was conducted on an anticyclonic, cold-core eddy located seaward of the Chukchi Shelf in the western Arctic Ocean. The eddy had a diameter of ∼16 km and was centered at a depth of ∼160 m between the 1000 and 1500 m isobaths over the continental slope. The water in the core of the eddy (total volume of 25 km3) was of Pacific origin, and contained elevated concentrations of nutrients, organic carbon, and suspended particles. The feature, which likely formed from the boundary current along the edge of the Chukchi Shelf, provides a mechanism for transport of carbon, oxygen, and nutrients directly into the upper halocline of the Canada Basin. Nutrient concentrations in the eddy core were elevated compared to waters of similar density in the deep Canada Basin: silicate (+20 μmol L−1), nitrate (+5 μmol L−1), and phosphate (+0.4 μmol L−1). Organic carbon in the eddy core was also elevated: POC (+3.8 μmol L−1) and DOC (+11 μmol L−1). From these observations, the eddy contained 1.25 × 109 moles Si, 4.5 × 108 moles NO3 −, 5.5 × 107 moles PO3 −, 1.2 × 108 moles POC, and 1.9 × 109 moles DOC, all available for transport to the interior of the Canada Basin. This suggests that such eddies likely play a significant role in maintaining the nutrient maxima observed in the upper halocline. Assuming that shelf-to-basin eddy transport is the dominant renewal mechanism for waters of the upper halocline, remineralization of the excess organic carbon transported into the interior would consume 6.70 × 1010 moles of O2, or one half the total oxygen consumption anticipated arising from all export processes impacting the upper halocline.This work was
supported by the National Science Foundation, and office of Naval
Research; DH OPP-0124900, NB OPP-0124868, DK OPP 0124872, RP
N00014-02-1-0317
Net community production in the northeastern Chukchi Sea
No full textTo assess the magnitude, distribution and fate of net community production (NCP) in the Chukchi Sea, dissolved inorganic carbon (DIC), dissolved organic carbon (DOC) and dissolved organic nitrogen (DON), and particulate organic carbon (POC) and particulate organic nitrogen (PON) were measured during the spring and summer of 2004 and compared to similar observations taken in 2002. Distinctive differences in hydrographic conditions were observed between these two years, allowing us to consider several factors that could impact NCP and carbon cycling in both the Chukchi Shelf and the adjacent Canada Basin. Between the spring and summer cruises high rates of phytoplankton production over the Chukchi shelf resulted in a significant drawdown of DIC in the mixed layer and the associated production of DOC/N and POC/N. As in 2002, the highest rates of NCP occurred over the northeastern part of the Chukchi shelf near the head of Barrow Canyon, which has historically been a hotspot for biological activity in the region. However, in 2004, rates of NCP over most of the northeastern shelf were similar and in some cases higher than rates observed in 2002. This was unexpected due to a greater influence of low-nutrient waters from the Alaskan Coastal Current in 2004, which should have suppressed rates of NCP compared to 2002. Between spring and summer of 2004, normalized concentrations of DIC in the mixed layer decreased by as much as 280 ?mol kg?1, while DOC and DON increased by ?16 and 9 ?mol kg?1, respectively. Given the decreased availability of inorganic nutrients in 2004, rates of NCP could be attributed to increased light penetration, which may have allowed phytoplankton to increase utilization of nutrients deeper in the water column. In addition, there was a rapid and extensive retreat of the ice cover in summer 2004 with warmer temperatures in the mixed layer that could have enhanced NCP. Estimates of NCP near the head of Barrow Canyon in 2004 were ?1500 mg carbon (C) m?2 d?1 which was ?400 mg C m?2 d?1 higher than the same location in 2002. Estimates of NCP over the shelf-break and deep Canada Basin were low in both years, confirming that there is little primary production in the interior of the western Arctic Ocean due to near-zero concentrations of inorganic nitrate in the mixed layer
Ross Mathis telegram to Joseph T. Robinson, February 18, 1928, related to flood control in the White River Levee District
No full textWestern Union telegram, two typed pages. Mathis notifies Senator Robinson of the financial exigencies of the White River Levee District.Ross Mathis (1890-1946) was an attorney from Cotton Plant, Arkansas
Ross Mathis letter to Joseph T. Robinson, February 13, 1928, related to flood control in the White River Levee District
No full textThree typed pages. Mr. Mathis writes to Senator Robinson regarding a potential refund of the monies the White River Levee District paid to the Mississippi River Commission and aid requested from the Red Cross. He also expresses his hope that future federal legislation would fund not only levee improvements on the Mississippi, but also those on tributaries such as the White River.Ross Mathis (1890-1946) was an attorney from Cotton Plant, Arkansas.[Page 3]
[Signature of Ross Mathis
2006 T&T Apprentice Students - Jeremy Williams
No full text2006 T&T Apprentice Students - Jeremy William
- …
