ALBERT

Description: The subarctic front (SAF) in the pelagic North Pacific is the northernmost front of the Kuroshio-Oyashio transition zone separating the subpolar and subtropical gyres and is marked by a strong sea surface temperature gradient. A complex interplay of e.g. variations of currents, the wind system and other forcing mechanisms causes shifts of the SAF’s position on timescales from orbital to interannual. In this study, we present proxy data from the Emperor Seamount chain, which reveal a link between long-term ENSO (El Niño/Southern Oscillation) dynamics in the tropics and shifts of the SAF. Based on sediment core SO264-45-2 from Jimmu Seamount (46°33.792’N, 169°36.072’E) located close to the modern position of the SAF, we reconstruct changes in (sub)surface temperature ((sub)SST Mg/Ca ) and δ 18 O sw-ivc (approximating salinities) via combined Mg/Ca and δ 18 O analyses of the shallow-dwelling foraminifera Globigerina bulloides and the near-thermocline-dwelling Neogloboquadrina pachyderma , biological productivity (XRF-based Ba/Ti ratios), and terrigenous input via dust (XRF-based Fe). From ~600 to ~280 ka BP we observe significantly higher SST Mg/Ca than after an abrupt change at 280 ka BP. We assume that during this time warmer water from the Kuroshio-Oyashio transition zone reached the core site, reflecting a shift of the SAF from a position at or even north of our study site prior to 280 ka BP to a position south of our study site after 280 ka BP. We propose that such a northward displacement of the SAF between 600-280 ka BP was induced by sustained La Niña-like conditions, which led to increased transport of tropical ocean heat into the Kuroshio-Oyashio transition zone via the Kuroshio Current. After ~280 ka BP, the change to more El Niño-like conditions led to less heat transfer via the Kuroshio Current with the SAF remaining south of the core location. In contrast, our productivity record shows a clear glacial-interglacial pattern that is common in the North Pacific. We assume that this pattern is connected to changes in nutrient supply or utilization, which are not primarily driven by changes of the Kuroshio and Oyashio Currents or the SAF.

Description: The North Pacific (NP) is an essential component of the global climate system as it acts as a significant natural carbon sink and neutralizes a part of the anthropogenic release of CO2. The efficiency of the NP carbon sink depends on a range of variable factors, including gyre circulation, the wind system, influences from tropical and subpolar regions, and internal reorganizations like stratification changes. Thus, a detailed investigation of the NP ocean-climate system of the past is crucial to understand how the ongoing climate change influences this region and will affect future global climate. This thesis, presents proxy records approximating (sub)-surface temperature (foraminiferal Mg/Ca), salinity (combined Mg/Ca and δ18), biological productivity (XRF based element ratios, CaCO3 content and alkenone concentrations) and terrigenous input via wind (XRF-based Fe) from a unique set of six sediment cores from a meridional transect from Hess Rise to the subarctic NP retrieved during R/V SONNE expeditions 202 and 264. The records reveal significantly different upper ocean conditions and a different productivity pattern in the western NP during the Pliocene than during the Pleistocene. This is associate with the intensification of Northern Hemisphere Glaciation, the onset of a permanent halocline and increased seasonality. Further, a different productivity and carbonate deposition/dissolution pattern of records south of 40°N compared to northern cores is linked to different nutrient regimes of the subtropical and subpolar gyre. Moreover, abrupt and pronounced changes in SST at site SO264-45 (e.g. at 480 ka and 280 ka) indicate shifts of the Subarctic Front induced by changes in the strength of the Kuroshio Extension, e.g., caused by sustained La Niña-like conditions in the tropical Pacific.

Description: Stable oxygen isotope (δ18O) measurements were performed on the benthic foraminiferal species C. wullerstorfi, Uvigeringa spp., and M. barleeanum as well as on the planktic foraminiferal species G. bulloides and N. incompta. Additionally Mg/Ca-measurements were performed on the two planktic species. The foraminiferal specimens were selected from gravity core SO264-45-2, which was recovered from Jimmu Seamount (46.5632°N 169.601211°E) from 2425 m water depth during R/V SONNE cruise SO264 (SONNE-EMPEROR) in August 2018. Sampling and analytical studies were carried out from 6.03 m – 8.32 m core depth at 2-4 cm spatial resolution. The isotope analyses were performed on a Thermo Scientific MAT 253 mass spectrometer with an automated Kiel IV carbonate preparation device. Trace metal analyses were performed on a VARIAN 720-ES Axial ICP-OES, a simultaneous, axial-viewing inductively coupled plasma - optical emission spectrometer coupled to a VARIAN SPS3 sample preparation system. Both systems were operated at GEOMAR. The proxy data provide stratigraphical information and were used to calculate water temperature and the ice volume-corrected δ18O of seawater. Contaminant phases of the trace metal analyses were added (Al/Ca, Fe/Ca, Mn/Ca in mmol/mol).

Description: Stable oxygen isotope (δ18O) measurements were performed on the benthic foraminiferal species C. wullerstorfi, Uvigerina spp., and M. barleeanum as well as on the planktic foraminiferal species G. bulloides, N. pachyderma and N. incompta. Additionally Mg/Ca-measurements were performed on the three planktic species. The foraminiferal specimens were selected from gravity core SO264-53-2, which was recovered from Minnetonka Seamount (47.648833°N 169.340283°E) from 2325 m water depth during R/V SONNE cruise SO264 (SONNE-EMPEROR) in August 2018. Sampling and analytical studies were carried out from 0.16-1.56 m and from 6.48-8.44 m core depth at 2-4 cm spatial resolution. The isotope analyses were performed on a Thermo Scientific MAT 253 mass spectrometer with an automated Kiel IV carbonate preparation device. Trace metal analyses were performed on a VARIAN 720-ES Axial ICP-OES, a simultaneous, axial-viewing inductively coupled plasma - optical emission spectrometer coupled to a VARIAN SPS3 sample preparation system. Both systems were operated at GEOMAR. The proxy data provide stratigraphical information and were used to calculate water temperature and the ice volume-corrected δ18O of seawater. Contaminant phases of the trace metal analyses were added (Al/Ca, Fe/Ca, Mn/Ca in mmol/mol).

Description: The dataset comprises X-ray fluorescence (XRF) measurements of the elements Titanium, Iron, Barium, Silicon, Calcium and the element ratios Barium/Titanium, Calcium/Titanium, and Silicon /Titanium of gravity core SO264-53-2. This core was recovered from Minnetonka Seamount (47.648833°N 169.340283°E) from 2325 m water depth during R/V SONNE cruise SO264 (SONNE-EMPEROR) in August 2018. XRF measurements reach from 0.16-1.56 m and from 6.48-8.47 m core depth. The measurements were carried out on an Avaatech XRF core scanner at the Alfred‐Wegener‐Institute Bremerhaven (AWI). Each segment was scanned at a 1 cm resolution.

Description: The dataset comprises X-ray fluorescence (XRF) measurements of the elements Titanium, Iron, Barium, Silicon, Calcium and the element ratios Barium/Titanium, Calcium/Titanium, and Silicon /Titanium of gravity core SO264-45-2. This core was recovered from Jimmu Seamount (46.5632°N 169.601211°E) from 2425 m water depth during R/V SONNE cruise SO264 (SONNE-EMPEROR) in August 2018. XRF measurements reach from 6.03 m – 8.27 m core depth and were carried out on an Avaatech XRF core scanner at the Alfred‐Wegener‐Institute Bremerhaven (AWI). Each segment was scanned at a 1 cm resolution.

Description: Stable carbon (δ13C) and oxygen isotope (δ18O) measurements were performed on the benthic foraminiferal species C. wullerstorfi and Uvigeringa spp. as well as on the planktic foraminiferal species G. bulloides and N. pachyderma. Additionally Mg/Ca-measurements were performed on the two planktic species. The foraminiferal specimens were selected from gravity core SO264-45-2, which was recovered from Jimmu Seamount (46.5632°N 169.601211°E) from 2425 m water depth during R/V SONNE cruise SO264 (SONNE-EMPEROR) in August 2018. Sampling and analytical studies were carried out from 0-3.44 m core depth at 2 cm spatial resolution. This interval covers the past ~650 ka BP. The isotope analyses were performed on a Thermo Scientific MAT 253 mass spectrometer with an automated Kiel IV carbonate preparation device. Trace metal analyses were performed on a VARIAN 720-ES Axial ICP-OES, a simultaneous, axial-viewing inductively coupled plasma - optical emission spectrometer coupled to a VARIAN SPS3 sample preparation system. Both systems were operated at GEOMAR. The proxy data provide stratigraphical information and were used to calculate water temperature and the ice volume-corrected δ18O of seawater. Contaminant phases of the trace metal analyses were added (Al/Ca, Fe/Ca, Mn/Ca in mmol/mol).

Description: The dataset comprises X-ray fluorescence (XRF) measurements of the elements Barium, Iron and Titanium of gravity core SO264-45-2, which was recovered from Jimmu Seamount (46.5632°N 169.601211°E) from 2425 m water depth during R/V SONNE cruise SO264 (SONNE-EMPEROR) in August 2018. XRF measurements comprise the upper 3.44 m of the core thereby covering the past ~650 ka BP and were carried out on an Avaatech XRF core scanner at the Alfred‐Wegener‐Institute Bremerhaven (AWI). Each segment was scanned at a 1 cm resolution. Here the barium/titanium (Ba/Ti) record is used as proxy for changes in paleoproductivity (biogenic barium) and the iron (Fe) record as proxy for relative changes in terrigenous input.