Mid Pleistocene productivity events in the subpolar NE Pacific: iron fertilization from aeolian dust and icebergs

• Main Authors: Müller, Juliane, Romero, Oscar E., Cowan, Ellen A., Forwick, Matthias, McClymont, Erin L., Asahi, Hirofumi, März, Christian, Suto, Itsuki, Mix, Alan C., Stoner, Joseph S.
• Format: Conference Object
• Language: unknown
• Published: Adam Mickiewicz University 2019
• Subjects: Gulf of Alaska; Pacific; Arctic; glaciers; Ice Sheet; North Atlantic; Alaska
• Online Access: https://epic.awi.de/id/eprint/52242/; http://palaeoarc.amu.edu.pl/wp-content/uploads/2019/05/PaleoArctic-Abstracts.pdf; https://hdl.handle.net/10013/epic.c135cf37-b4c1-4011-8606-74e91e86116f

IODP Expedition 341 succeeded in recovering a continuous sedimentary record of Miocene to Late Pleistocene climate history at drill Site U1417 in the Gulf of Alaska, NE Pacific. Site U1417 sediments provide an excellent opportunity to reconstruct North Pacific sea surface conditions during late Neogene large-scale (global) climate transitions. The Mid Pleistocene Transition (MPT) - one of the most prominent intervals of global Quaternary climate change - is clearly identifiable in Site U1417 sediments (Jaeger et al., 2014). To fully exploit the environmental information archived in U1417 sediments, a sampling strategy has been pursued that permits direct correlation of different (independent) proxy data obtained from biomarker, micropalaeontological, sedimentological and geochemical (XRF) analyses. Mid Pleistocene SSTs in the Gulf of Alaska are in good agreement with SST reconstructions for the North Atlantic and the NW Pacific. A general cooling at about 1 Ma supports earlier hypotheses of an overall Northern Hemisphere ocean cooling as a prerequisite for the increase in continental ice volume. While phytoplankton productivity seems rather independent from SST at Site U1417, it is strongly related to elevated TAR values depicting enhanced input of terrestrial leaf-wax lipids (Meyers, 1997). The transport of these lipids is supposed to be effected by strong winds carrying dust from Alaskan loess deposits to the open ocean as well as by icebergs released from Alaskan tidewater glaciers. The latter is supported by the occasional coincidence of high IRD contents and TAR values. The close relationship between the TAR record, Ba/Al values and the abundance of diatoms, however, strengthens that together with the leaf-wax lipids also iron-bearing dust was exported leading to high productivity events at Site U1417 throughout the Mid Pleistocene. The distinct "on-off" pattern in diatom productivity evolved with the onset of the MPT, which suggests that the expansion of the Northwest Cordilleran Ice Sheet lead to an effective production of glacigenic iron-rich dust that was exported i) by strong northwesterly winds and ii) by icebergs. The observation that productivity peaks in the Gulf of Alaska are not confined to glacial or interglacial periods points to a rather local feedback between the export of iron-bearing dust and an immediately responding ocean surface. The identification of these hitherto unconsidered fertilization mechanisms that potentially fostered ocean productivity and hence the sequestration of atmospheric carbon into the deep ocean are further detailed by Müller et al. (2018).