Orbital and suborbital variations of productivity and sea surface
conditions in the Gulf of Alaska during the past 54,000 years: Impact of
iron fertilization by icebergs and meltwater
Abstract
As a high-nutrient and low-chlorophyll region, the modern Gulf of Alaska
(GoA) is strongly impacted by the limitation of iron. Paleostudies along
the Alaskan slope have mainly focused on reconstructing environmental
conditions over the past 18 ka. Based on micropaleontological,
biogeochemical and sedimentological parameters, we explore a sediment
record covering the past 54 ka at Integrated Ocean Drilling Program Site
U1419 to understand the impact of orbital and suborbital-scale climate
variability on productivity and sea-surface conditions. Close to the
Cordilleran Ice Sheet (CIS), Site U1419 is ideally located to elucidate
how the evolution of a large ice mass and glacial processes affected
orbital- and suborbital-scale changes in nutrients-(e.g., iron)
supply. Meltwater discharge from the northern CIS impacted sea surface
dynamics of GoA coastal waters. The corresponding increase in bulk
biogenic concentrations during Marine Isotope Stage (MIS) 3 and MIS 2
(54 – 17.3 ka) suggests a direct impact from iron fertilization.
Cooling of surface waters played no primary role in the occurrence of
primary producers. The inundation of the subaerially exposed continental
shelf during the last deglacial (17.3-10 ka) warming could have served
as a major micronutrients source. Low productivity after the last
deglaciation suggests reduced iron availability. Our multiproxy approach
reveals a more complete picture of late Quaternary productivity
variations compared to earlier studies along the Alaskan margin. The
impact of tidewater glaciers and meltwater discharge on past marine
productivity and nutrient budget dynamics of high-latitude coastal
regions is discussed.