Iron counts from XRF scanning positively correlated with the deglacial paleoproductivity in the Gulf of Alaska

In the Gulf of Alaska (GoA), the productivity during the Bølling-Allerød (BA) and in the early Holocene may influence by the supply of Fe from the continental shelves due to the deglacial sea-level rise (Davies et al., 2011). Lam et al., 2013 suggested that no evidence for an abrupt deglacial Fe during peak productivity. To test these hypotheses, we examine a high-resolution XRF record in this experiment.

We generated a high-resolution XRF core scanner data together with a multiple set of destructive geochemical data, such as planktonic foraminiferal oxygen and carbon isotope, carbon and nitrogen contents, molecular biomarker, ice rafting debris and Sr-Nd isotopes of bulk sediments from the core CL14PC in the GoA (59° 33.35´N, 144° 09.35´W, water depth 690 m). The ¹⁴C dates from mixed planktonic foraminifers were used for age-depth model construction.

By comparing different correction methods, we found that the downcore XRF element data concord reasonably well with the conventional method. The XRF intensity of the high resolute (0.4 mm) Fe was higher in the BA (14.8-13 cal. ka BP) and in the Preboreal (PB, 11.7-10.8 cal. ka BP) compared to the Younger Dryas (14.8-13 cal. ka BP) and in the Heinrich Stadial 1 (17-14.8 cal. ka BP). We observed two peak productivity episodes at BA and PB marked by elevated Br and TOC-rich laminated sediments synchronized with high XRF Fe.

During the BA and PB periods, the high fluxes of deglacial meltwater with suspended sediment delivered terrestrially derived nutrients (Fe, P, Si) to the coastal ocean. The coastal region of the GoA is a depocenter where an abundance of terrigenous Fe load was deposited. These loads undergo different physical, chemical, and biological processes, produce an isotopically light Fe pool that transferred to the water column, and make it accessible for surface biota. Besides, the deglacial meltwater from the decay of the Cordilleran Ice Sheet caused the abrupt sea-level rise that inundated the coastal depocenters and increases the supply of Fe through remobilization. The resultant Fe triggered productivity during the periods (BA and PB).

Our findings indicating high XRF Fe during the deglacial peak productivity episodes, that (Fe) transported with high deglacial meltwater and remobilization and positively correlated with the paleoproductivity in the Gulf of Alaska.