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  • 2020-2024  (3)
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  • 1
    Publication Date: 2024-01-18
    Description: The North Atlantic Basin is a major sink for atmospheric carbon dioxide (CO2) due in part to the extensive plankton blooms which form there supported by nutrients supplied by the three-dimensional ocean circulation. Hence, changes in ocean circulation and/or stratification may influence primary production and biological carbon export. In this study, we assess this possibility by evaluating inorganic nutrient budgets for 2004 and 2010 in the North Atlantic based on observations from the transatlantic A05-24.5°N and the Greenland-Portugal OVIDE hydrographic sections, to which we applied a box inverse model to solve the circulation and estimate the across-section nutrient transports. Full water column nutrient budgets were split into upper and lower meridional overturning circulation (MOC) limbs. According to our results, anomalous circulation in early 2010, linked to extreme negative NAO conditions, led to an enhanced northward advection of more nutrient-rich waters by the upper overturning limb, which resulted in a significant nitrate and phosphate convergence north of 24.5°N. Combined with heaving of the isopycnals, this anomalous circulation event in 2010 favored an enhancement of the nutrient consumption (5.7 ± 4.1 kmol-P s−1) and associated biological CO2 uptake (0.25 ± 0.18 Pg-C yr−1, upper-bound estimate), which represents a 50% of the mean annual sea–air CO2 flux in the region. Our results also suggest a transient state of deep silicate divergence in both years. Both results are indicative of a MOC-driven modulation of the biological carbon uptake (by the upper MOC limb) and nutrient inventories (by the lower MOC limb) in the North Atlantic.
    Repository Name: EPIC Alfred Wegener Institut
    Type: Article , isiRev
    Format: application/pdf
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  • 2
    Publication Date: 2023-06-23
    Description: The coastal ocean, the interface between the land and sea is a key environment for the biogeochemical cycling of carbon, yet these heterogeneous environments are historically under sampled. It is now becoming apparent that anthropogenic CO〈sub〉2〈/sub〉 induced ocean acidification is an open ocean syndrome and that ocean acidification in the coastal environments is far more complex. In the coastal ocean several processes will drive CO〈sub〉2〈/sub〉 trends, such as seawater temperature, biological processes, residence time and air to sea gas exchange. We investigate the distribution and fate of inorganic carbon in a tropical coastal environment, influenced by riverine discharge and local marine habitats – coral reefs, seagrass beds and mangroves. The Belize River, which drains the largest catchment in Belize, discharges just north of Belize City and is a source of high pCO〈sub〉2〈/sub〉 (〉2000 µatm) water to the coastal environment. We investigate the process that occur once this low pH (〈7.6) water enters the coastal ocean and whether this low pH water, which is corrosive to corals (Ω〈sub〉arag〈/sub〉 〈1), reaches the barrier reef. Using a combination of sensor measurements and discrete samples, we found no evidence that river water reaches the barrier reef, located ~20km offshore. This was due to a number of processes occurring in the coastal ocean, including outgassing of CO〈sub〉2〈/sub〉 to the atmosphere and high rates of photosynthesis taking place, likely from benthic seagrass beds.
    Language: English
    Type: info:eu-repo/semantics/conferenceObject
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  • 3
    Publication Date: 2023-07-01
    Description: It is important to understanding the mechanism behind multidecadal changes in North Atlantic ocean heat storage as these directly impact the climate of the surrounding continents. We construct a multidecadal upper ocean heat budget for the North Atlantic for the period 1950 to 2020 based on multiple observational datasets and a state of the art forced global ocean model. On multidecadal timescales ocean heat transport convergence is the dominant term in all regions of the North Atlantic. In the subpolar region (north of 45N) the heat transport convergence is largely explained by anomalous geostrophic currents acting on the mean temperature gradient. The timescale and spatial distribution of the anomalous geostrophic currents are consistent with basin scale ‘thermal’ Rossby waves propagating westwards/northwestwards in the subpolar gyre. Using a forced ocean model we link the ocean heat transport convergence with variations in the Atlantic Meridional Overturning Circulation.
    Language: English
    Type: info:eu-repo/semantics/conferenceObject
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