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Abstract
Abstract. Marine sediments records suggest large changes in marine productivity during glacial periods, with abrupt variations especially during the Heinrich events. Here, we study the response of marine biogeochemistry to such an event by using a biogeochemical model of the global ocean (PISCES) coupled to an ocean-atmosphere general circulation model (IPSL-CM4). We conduct a 400-yr-long transient simulation under glacial climate conditions with a freshwater forcing of 0.1 Sv applied to the North Atlantic to mimic a Heinrich event, alongside a glacial control simulation. To evaluate our numerical results, we have compiled the available marine productivity records covering Heinrich events. We find that simulated primary productivity and organic carbon export decrease globally (by 16% for both) during a Heinrich event, albeit with large regional variations. In our experiments, the North Atlantic displays a significant decrease, whereas the Southern Ocean shows an increase, in agreement with paleo-productivity reconstructions. In the Equatorial Pacific, the model simulates an increase in organic matter export production but decreased biogenic silica export. This antagonistic behaviour results from changes in relative uptake of carbon and silicic acid by diatoms. Reasonable agreement between model and data for the large-scale response to Heinrich events gives confidence in models used to predict future centennial changes in marine production. In addition, our model allows us to investigate the mechanisms behind the observed changes in the response to Heinrich events.
Highlights
Marine primary productivity (PP) is a key component of climate-active biogeochemical cycles such as the carbon cycle
Our model has a parameterization of Si/C as a function of temperature and iron availability that is not implemented in LOVECLIM and we have shown in the results section that this parameterization was key to simulate the East Equatorial Pacific (EEP) region changes
This study shows that the model IPSL-CM4 including PISCES is able to represent the main features of EXP response to a Heinrich events (HEs), except for the Mauritanian region which needs to be further investigated
Summary
Marine primary productivity (PP) is a key component of climate-active biogeochemical cycles such as the carbon cycle. A reduced input of nutrients to the euphotic zone from subsurface waters due to increased stratification decreases PP in the North Atlantic and tropical regions, whereas lower light limitation increases Southern Ocean PP (Bopp et al, 2001; Steinacher et al, 2010). Another model (Schmittner et al, 2008) shows an increase in PP and a decrease in EXP due to enhanced remineralisation in response to increasing temperature. Evaluation of these models on such decadal-to-centennial time scales is still difficult due to sparse data covering these time scales (Schneider et al, 2008) and relatively moderate climatic change
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