THE ROLE OF THE ALASKA COASTAL CURRENT IN HOLOCENE PRIMARY PRODUCTIVITY IN SOUTHEAST ALASKA FJORDS
These phytoplankton patterns are compared against geochemical proxies for both nearshore and offshore ACC strength. X-ray fluorometry (XRF)-based proxies of detrital run-off from the coastal fjord records indicate the highest run-off rates during the early Holocene, which decline to near-modern levels between 6 and 7 cal ka BP. An offshore ACC record reveals strong ACC flow during the early Holocene (>8 cal ka BP) and oscillatory behavior during the middle and late Holocene (~6 to <1 cal ka BP). Taken together, the offshore and nearshore ACC records suggest: (1) a shared mechanism affecting the ACC during the early Holocene, possibly related to the decay of the Cordilleran Ice Sheet and coastal release of stored sediments; and (2) the divergence in nearshore and offshore ACC patterns during the middle and late Holocene imply the nearshore ACC is less dynamic relative to the offshore sector of the ACC. These findings imply coastal fjord productivity in Southeast Alaska likely responds to non-ACC influences, such as the subsurface delivery of macronutrient-rich HNLC waters from the open GoAK, which is in turn influenced by regional atmosphere-ocean interactions.