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)SSTMg/Ca) and δ18Osw-ivc (approximating salinities) via combined Mg/Ca and δ18O 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 SSTMg/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.

<p>At present, the North Pacific constitutes one of the main marine natural carbon sinks and thus helps regulate atmospheric CO<sub>2 </sub>concentrations. Understanding past changes in North Pacific deep water circulation and biological productivity are of particular importance, since the region likely changed these characteristics on both orbital and millennial time scales, and may have even undergone switches between being a carbon source and sink. We present a suite of new sediment records retrieved from the subarctic Northwest Pacific along the Emperor Seamount Chain in order to contribute to the Pleistocene stratigraphy and reconstruct changes in the physical and biological carbon pump on millennial to orbital timescales. We used high-resolution AMS 14C-derived benthic-planktic (B-P) foraminiferal ventilation ages, and stable carbon and oxygen isotopes of epibenthic foraminifera along both meridional and water depth transects in order to establish deep water ventilation patterns and reconstruct nutrient concentrations over the last 200 ka. We used X-ray fluorescence (XRF)-scanning records combined with radiocarbon dating to correlate prominent patterns between sediment cores, and to develop a stratigraphic framework for the study area. We used changes in Ba/Ti, Ca/Ti, Si/Ti ratios to assess variationsin biological productivity. Biogenic Barium (Ba/Ti) and Calcium (Ca/Ti) ratios generally show high values during interglacials and low values during glacials. This pattern resembles subpolar Northwest Pacific ODP Site 882, which shows a good correlation to the global CO<sub>2 </sub>record. These results provide evidence for the close link between global climate, the ocean carbon cycle and marine biogeochemistry in North Pacific.</p>

<p>The North Pacific plays a key role in shaping the Earth’s climate, yet there still is a lack in understanding the complex interplay of atmosphere and ocean, and their respective circulation patterns reacting to a varying Pleistocene climate. Proxy records established on marine sediment core SO264-28-2, recovered from the Emperor Seamount Chain (Suiko Seamount; ~45°N, close to the Subarctic Front) during R/V SONNE Cruise SO264 in 2018, allow to reconstruct changes of surface and subsurface water masses in order to provide unique insight in spatial and temporal shifts of North Pacific Subarctic<em> vs.</em> Subtropical gyres. According to the preliminary age model based on radiocarbon dating, benthic oxygen isotopes, combined magneto-, tephra- and biostratigraphical approaches, the only 7 m long core covers the last ~1.35 Myr. This core was chosen due to its highly characteristic pattern in magnetic susceptibility and a prominent lithological change from carbonate oozes to more siliciclastic sediment sequences at ~1.2 Ma. Thus, numerous other cores from the study area can be correlated with it suggesting this core as a reference record for the North Pacific.</p><p>A continuous and synchronous cooling of both surface and subsurface ocean temperatures since ~1.35 Ma changed rapidly at 1.2 Ma to a continuous warming surface from <4 °C to ~ 8 °C while subsurface temperature remained constant below 4 °C. The long-term diverging temperatures and increasing salinities at both surface and subsurface point to the continuous northward displacement of the Subarctic Front and an increased influence of the North Pacific Tropical Water at Suiko Seamount, with most prominent, millennial-scale, changes of the gyre system and the related Kuroshio Current during interglacials. Around ~430 ka, the influence of warm and saline subtropical surface water masses declines, reflected by a rapid decrease of sea surface temperatures of 4-5 °C and a salinity inversion, whereby the subsurface water mass becomes more saline than the surface water. After ~430 ka, interglacials are very pronounced and with the prominent presence of low saline and cooler surface waters, conditions are similar to present.</p>

<p>The subarctic front (SAF) in the pelagic Pacific Ocean is the northernmost front that separates the Oyashio Current, which marks the southern boundary of the subpolar gyre, from the Kuroshio Current, the northern boundary of the subtropical gyre. Its strong sea surface temperature (SST) gradient is not a stable and permanent feature but shifts on timescales from interannual to glacial/interglacial. Yet the complex interplay of different driving mechanisms for this phenomenon is not yet entirely understood. In this study, we present newly retrieved data from the Emperor Seamount chain that reveals a link between long-term ENSO (El Niño /Southern Oscillation) dynamics in the tropics and shifts of the SAF. Here, we use marine sediment core SO264-45-2 (46°33.792’N, 169°36.072’E), recovered from the Emperor Seamount Chain during R/V SONNE Cruise SO264 in 2018 to reconstruct changes in (sub-) surface temperature and salinity via a combined Mg/Ca and δ<sup>18</sup>O analyses of the shells of the shallow living planktic foraminifera <em>Globigerina bulloides</em> and the near thermocline living <em>Neogloboquadrina pachyderma</em>. This reveals that SST and salinity do not show a clear glacial/interglacial pattern during the last 280 ka and thus we assume that the SAF was south of the core site during this time interval. Prior to 280 ka, SSTs were significantly higher and show greater amplitudes than after 280 ka, while the subsurface temperature stayed relatively constant. Such high SSTs together with the observed higher sea surface salinities prior to 280 ka indicate that water from the Kuroshio-Oyashio transition zone temporarily reached the core site in form of a warm surface water lens. This points to a northward displacement of the SAF of at least 5° so that it was located right above the core site. This way very small north and southward displacements e.g. in relation to glacial/interglacial periods would have caused SST changes as high as we observe them in the time interval 280-700 ka. Notably, this assumed shift of the SAF at 280 ka occurs simultaneously to a change from more La Niña-like to more El Niño-like conditions in the tropical Pacific. Moreover, warm phases in the time interval 280-700 ka seem to occur during times of more La Niña-like conditions in the tropics, while cold phases seem to be related to more El Niño-like conditions. As our study area is linked to the subtropical gyre via the Kuroshio Current, we assume that the observed shifts of the SAF at our study site were caused by the enhancement of the Kuroshio Current in time intervals of more La Niña-like like conditions.</p>