The role of Patagonian Dust-Fe in fertilisation of the Southern Ocean
Although Antarctic ice cores show relative agreement on dust flux over the last glacial cycle, the same cores show marked differences in Methane Sulphonic Acid (MSA) deposition – commonly regarded as a proxy for oceanic phytoplankton growth – over the same period. This contradiction has complicated our understanding of the fertilisation effect of dust on the High-Nutrient Low-Chlorophyll (HNLC) Fe-limited Southern Ocean. The uncertainty surrounds whether it is dust fertilisation, or another mechanism such as marine nutrient upwelling, or changes in temperature and/or solar radiation, which is the main factor driving primary productivity in this region. If dust fertilisation is important, why is it that in some ice cores dust and MSA deposition is correlated, while in others they are out of phase? Questions such as these have fuelled doubt over the precise role of dust in ocean fertilisation.
We present new, contemporary, ice core evidence of event-scale correlations between dust Fe and MSA deposition in the high latitude South Atlantic Ocean. This suggests there is a strong relationship between dust and HNLC ocean fertilisation in this region at the present time, that is, dust fertilisation is a major driver of marine productivity. The difference between this finding and the variability in the MSA/dust flux relationship over glacial/interglacial time periods implies that while dust deposition drives event/centennial scale ocean productivity under current climate conditions, over longer time periods the relationship is less clear. Because our results imply dust emissions are linked to marine productivity over the recent past we use dust deposition data from Patagonian peat cores to explore what impact dust may have had on oceanic fertilisation during the Holocene and Anthropocene.