Abstract
Abstract. Increased transfer of particulate matter from continental shelves to the open ocean during glacials may have had a major impact on the biogeochemistry of the ocean. Here, we assess the response of the coupled oceanic cycles of oxygen, carbon, phosphorus, and iron to the input of particulate organic carbon and reactive phosphorus from shelves. We use a biogeochemical ocean model and specifically focus on the Last Glacial Maximum (LGM). When compared to an interglacial reference run, our glacial scenario with shelf input shows major increases in ocean productivity and phosphorus burial, while mean deep-water oxygen concentrations decline. There is a downward expansion of the oxygen minimum zones (OMZs) in the Atlantic and Indian Ocean, while the extension of the OMZ in the Pacific is slightly reduced. Oxygen concentrations below 2000 m also decline but bottom waters do not become anoxic. The model simulations show when shelf input of particulate organic matter and particulate reactive P is considered, low oxygen areas in the glacial ocean expand, but concentrations are not low enough to generate wide scale changes in sediment biogeochemistry and sedimentary phosphorus recycling. Increased reactive phosphorus burial in the open ocean during the LGM in the model is related to dust input, notably over the southwest Atlantic and northwest Pacific, whereas input of material from shelves explains higher burial fluxes in continental slope and rise regions. Our model results are in qualitative agreement with available data and reproduce the strong spatial differences in the response of phosphorus burial to glacial-interglacial change. Our model results also highlight the need for additional sediment core records from all ocean basins to allow further insight into changes in phosphorus, carbon and oxygen dynamics in the ocean on glacial-interglacial timescales.
Highlights
Phosphorus (P) is an essential nutrient in marine biogeochemistry and is believed to limit primary productivity on geological timescales (Tyrrell, 1999)
Our results show that shelf input of particulate organic matter and particulate inorganic P can significantly impact ocean productivity, deep-water oxygen and, in contrast to what was suggested in previous modeling work, burial of reactive P in the global ocean
Because the dynamics of the fixation to organic matter (Fe) cycle were not included in previous versions of the model (Palastanga et al, 2011), here we briefly describe the most relevant results of the model reference run
Summary
Phosphorus (P) is an essential nutrient in marine biogeochemistry and is believed to limit primary productivity on geological timescales (Tyrrell, 1999). Variations in P availability in the open ocean have the potential to impact primary productivity and ocean oxygenation during glacials. P burial on shelves was likely reduced because of sea level fall, whereas the erosive transfer of particulate material containing reactive P and degradable carbon from shelves to the open ocean was likely enhanced (Ruttenberg, 1993). The inventory of P in the open ocean, primary productivity and CO2 drawdown may have increased, whereas ocean oxygen may have declined. This potential impact on productivity and CO2 was first brought forward by Broecker (1982) in the so-called shelf-nutrient hypothesis
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