Sedimentary proxies for Pacific water inflow through the Herald Canyon, western Arctic Ocean

Abstract

Pacific water inflow to the Arctic Ocean occurs through the shallow Bering Strait. With a present sill depth of only 53 m, this gateway has been frequently closed during glacial sea-level low stands of the Pleistocene. Here, we investigate the sedimentological and mineralogical response to sea-level rise and the opening of the Bering Strait during the last deglaciation in a 6.1 m-long marine sediment core (SWERUS-L2-4-PC1) from the Herald Canyon. Grain size data indicate an abrupt erosional contact at 412 cm down core that likely formed when Pacific waters first started to flow into the Arctic Ocean around 11 cal ka BP, and was topographically steered into the Herald Canyon. A transitional unit between 412 and 390 cm appears to be a condensed interval with minimal local sedimentation. The underlying sediments, deposited in a shallow, river-proximal setting, exhibit a rather uniform bulk and clay mineral composition similar to mineral assemblages from surface sediment samples of the Chukchi Sea. Enhanced contributions from Pacific waters above 390 cm (< 8.5 cal ka BP) are reflected by elevated chlorite/illite and (chlorite + kaolinite)/illite ratios, and are anti-correlated with intervals of higher illite/smectite ratios, interpreted as periods of enhanced advection of shelf transformed waters originating from the East Siberian Sea. Clay mineral changes in the Holocene drift sediments are best explained by the interplay between two origins for bottom waters in the Herald Canyon and are consistent with modern oceanographic observations.

Late Holocene Paleomagnetic Secular Variation in the Chukchi Sea, Arctic Ocean

“…Grain size data from Swärd et al. (2018). Red dashed lines on the ChRM inclination plots represent 81°, the expected inclination at the coring site for a geocentric axial dipole.…”

“…As they move northward, these water masses modulate the sedimentation regime of the area. For example, surface sediments from the Chukchi Sea presently are enriched in chlorite and smectite, and have generally high organic carbon (1.5%–2.8% ‐ Stein et al., 2004) and biogenic silica contents (>10% wt), a direct result of inflowing Pacific waters and high seasonal biological productivity (e.g., Swärd et al., 2018). A distinct branch of Pacific waters heads north via the Herald Canyon, an underwater area at the north‐western part of the Chukchi Sea (Figure 1).…”

“…Although only separated by 38 km, the depositional settings of 2‐PC1 and 4‐PC1 are quite different. The sediments of 2‐PC1 are mainly hemipelagic in nature, while core 4‐PC1 sampled sediments from a drift deposit (Jakobsson et al., 2017; Swärd et al., 2018). The water depth at the coring site of 4‐PC1 (120 m) is approximately twice that of 2‐PC1 (57 m), which means that Atlantic sourced waters are sometimes present at the former site and results in different ∆R values for regional marine reservoir age correction (Cronin et al., 2017; Jakobsson et al., 2017; Pearce et al., 2017).…”

“…Star-Oddi ® orientation and tilt sensors were attached to the outside of the piston core barrels to monitor tilt through core penetration (O'Regan et al, 2016) (Figure S1a in Supporting Information S1). The cores are composed of gray-olive gray sediments, which have a low and sporadic abundance of calcareous microfossils and mollusks (Seidenstein et al, 2018), and relatively high biogenic silica (∼15% - Swärd et al, 2018) and total organic carbon (TOC) content (0.74%-2.38% - Martens et al, 2019). Detailed descriptions of core sampling, curation, and physical properties measurements were presented by Cronin et al (2017), Jakobsson et al (2017), andPearce et al (2017).…”

Arctic environmental change beyond instrumental records: introduction and overview

“…Swärd et al [6] use sedimentary proxies to study Pacific water inflow to the Arctic Ocean through the shallow Bering Strait after the LGM. They find that the first inflow of Pacific water occurred around 11 cal ka BP.…”