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The ocean holds vast quantities of carbon that it continually exchanges with the atmosphere through the air-sea interface. Because of its enormous size and relatively rapid exchange of carbon with the atmosphere, the ocean controls atmospheric CO 2 concentration and thereby Earth's climate on timescales of tens to thousands of years. This review examines the basic functions of the ocean's carbon cycle, demonstrating that the ocean carbon inventory is determined primarily by the mass of the ocean, by the chemical speciation of CO 2 in seawater, and by the action of the solubility and biological pumps that draw carbon into the ocean's deeper layers, where it can be sequestered for decades to millennia. The ocean also plays a critical role in moderating the impacts of climate change by absorbing an amount of carbon equivalent to about 25% of anthropogenic CO 2 emissions over the past several decades. However, this also leads to ocean acidification and reduces the chemical buffering capacity of the ocean and its future ability to take up CO 2 . This review closes with a look at the uncertain future of the ocean carbon cycle and the scientific challenges that this uncertainty brings.
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Evidence from the subtropical North Atlantic Ocean for the influence of iceberg discharge on ocean circulation and climate during the last ice age
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Abstract. Global- and basin-scale ocean reanalyses are becoming easily accessible and are utilized widely to study the Southern Ocean. However, such ocean reanalyses are optimized to achieve the best model–data agreement for their entire model domains and their ability to simulate the Southern Ocean requires investigation. Here, we compare several ocean reanalyses (ECCOv4r5, ECCO LLC270, B-SOSE, and GECCO3) based on the Massachusetts Institute of Technology General Circulation Model (MITgcm) for the Southern Ocean. For the open ocean, the simulated time-mean hydrography and ocean circulation are similar to observations. The MITgcm-based ocean reanalyses show Antarctic Circumpolar Current (ACC) levels measuring approximately 149 ± 11 Sv. The simulated 2 °C isotherms are located in positions similar to the ACC and roughly represent the southern extent of the current. Simulated Weddell Gyre and Ross Gyre strengths are 51 ± 11 and 25 ± 8 Sv, respectively, which is consistent with observation-based estimates. However, our evaluation finds that the time evolution of the Southern Ocean is not well simulated in these ocean reanalyses. While observations showed little change in open-ocean properties in the Weddell and Ross gyres, all simulations showed larger trends, most of which are excessive warming. For the continental shelf region, all reanalyses are unable to reproduce observed hydrographic features, suggesting that the simulated physics determining on-shelf hydrography and circulation is not well represented. Nevertheless, ocean reanalyses are valuable resources and can be used for generating ocean lateral boundary conditions for regional high-resolution simulations. We recommend that future users of these ocean reanalyses pay extra attention if their studies target open-ocean Southern Ocean temporal changes or on-shelf processes.more » « less
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