A mid-Holocene geochemical record of saline inflow to the Gotland Deep, Baltic Sea

The formation of Mn-enrichments in Gotland Deep sediments has been linked to the occurrence of periodic inflows of saline water from the North Sea. In turn these saline inflow events are very strongly linked to variation in North Atlantic atmospheric conditions. Here sedimentary Mn-concentrations in mid-Holocene sediments are measured with a 0.5 mm sampling resolution using scanning electron microscope techniques. As the sedimentation rate in core 20001-5 was estimated to be approximately 0.5–1 mm per year, examining the variation in Mn-enrichments may potentially provide an annual record of variation in saline inflow, and by extension, North Atlantic climate on interannual timescales. There are many processes that can affect Mn-cycling in the Gotland Deep. When considered together, these processes could potentially act to remove or significantly weaken the transmission of the primary saline inflow signal to the measured geochemical record, producing an effectively random Mn-record. Analysis of the Mn-record as a time series of discrete events revealed that the Mn-record was not consistent with a random distribution of events, and contains some long-term order. Spectral analysis of the Mn-record then indicates a significant periodicity in the Mn-record between 33 and 35.5 mm. This represents a discrete decadal periodicity in Mn-enrichment at 25–55 years that is consistent with the timing of previously reported Mn-enrichments in Gotland Deep sediments