ALBERT

Description: We investigated benthic foraminifera in cores GPC03 and GPC04 in the northeast tropical Indian Ocean (TIO) over the past ~450 ka to evaluate the ballasting effect of particulate organic matter (POM) and the long-term zonal change during the mid-Brunhes dissolution interval (MBDI). Today, interannual climate and oceanographic variability in the TIO is governed by the Indian Ocean Dipole (IOD), which manifests as asymmetric zonal oceanographic change. Here we provide our sediment geochemical, stable oxygen and carbon isotope data and faunal data of benthic foraminifera in core GPC04.

Description: We investigated benthic foraminifera in cores GPC03 and GPC04 in the northeast tropical Indian Ocean (TIO) over the past ~450 ka to evaluate the ballasting effect of particulate organic matter (POM) and the long-term zonal change during the mid-Brunhes dissolution interval (MBDI). Today, interannual climate and oceanographic variability in the TIO is governed by the Indian Ocean Dipole (IOD), which manifests as asymmetric zonal oceanographic change. Here we provide our sediment geochemical, stable oxygen and carbon isotope data and faunal data of benthic foraminifera in core GPC04.

Description: By means of a multiproxy data set combining biomarker (alkenones, n-alkanes), microfossil (diatoms) and sedimentological (ice rafted debris, XRF) data obtained from sediments from IODP Site U1417 in the Gulf of Alaska, we elucidate the paleoenvironmental setting in this area during the Mid Pleistocene Transition. The data point to a stimulation of the marine primary productivity through the input of nutrients (e.g. iron) via aeolian dust and icebergs. These fertilization pulses were likely triggered by the dynamic behaviour of the Cordilleran Ice Sheet during the Pleistocene.

Description: IODP site U1417 in the Gulf of Alaska provides a continuous sedimentary record of environmental changes (e.g., in sea surface temperature (SST), marine productivity, ice-rafting) in the subpolar NE Pacific through the Plio-Pleistocene time interval. Here, we present a multi-proxy data set, which allows us to discriminate between different fertilization mechanisms that promoted primary productivity events in the study area between 1.5 Ma and 0.5 Ma. Based on biomarker, micropaleontological, XRF, and sedimentological data, we find that diatom growth benefited from iron-fertilization from aeolian dust, iceberg, and volcanic ash input. Glacial-interglacial SST fluctuations were superimposed by a slight cooling trend with a first pronounced temperature drop during MIS 38 and significantly lowered SSTs persisting through MIS 30 and MIS 28. While the diatom productivity pulses were mainly independent from SST changes, they coincide with terrigenous organic matter input and their occurrence during both glacial and interglacial periods suggest that iron supply from glacigenic dust was mainly controlled by local ice-sheet dynamics. This data set highlights the complexity of fertilization mechanisms in areas affected by evolving ice-sheets and their potential control on the biological carbon pump in subpolar ocean environments.

Description: 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).

Description: Erosion, sediment production, and routing on a tectonically active continental margin reflect both tectonic and climatic processes; partitioning the relative importance of these processes remains controversial. Gulf of Alaska contains a preserved sedimentary record of the Yakutat Terrane collision with North America. Because tectonic convergence in the coastal St. Elias orogen has been roughly constant for 6 My, variations in its eroded sediments preserved in the offshore Surveyor Fan constrain a budget of tectonic material influx, erosion, and sediment output. Seismically imaged sediment volumes calibrated with chronologies derived from Integrated Ocean Drilling Program boreholes show that erosion accelerated in response to Northern Hemisphere glacial intensification (∼2.7 Ma) and that the 900-km-long Surveyor Channel inception appears to correlate with this event. However, tectonic influx exceeded integrated sediment efflux over the interval 2.8–1.2 Ma. Volumetric erosion accelerated following the onset of quasi-periodic (∼100-ky) glacial cycles in the mid-Pleistocene climate transition (1.2–0.7 Ma). Since then, erosion and transport of material out of the orogen has outpaced tectonic influx by 50–80%. Such a rapid net mass loss explains apparent increases in exhumation rates inferred onshore from exposure dates and mapped out-of-sequence fault patterns. The 1.2-My mass budget imbalance must relax back toward equilibrium in balance with tectonic influx over the timescale of orogenic wedge response (millions of years). The St. Elias Range provides a key example of how active orogenic systems respond to transient mass fluxes, and of the possible influence of climate-driven erosive processes that diverge from equilibrium on the million-year scale.