On the reconstruction of ocean circulation and climate based on the “Gardar Drift”

Abstract

Sediment-based reconstructions of bottom water velocity at the Gardar Drift are commonly interpreted to reflect changes in the eastern Nordic Seas overflows. Here we investigate the relationship between changes in the water that overflows through the Faroe Shetland Channel and downstream bottom velocity at the location of the Gardar Drift as represented in a 500 year long simulation with the Bergen Climate Model. We identify a region in our simulation proximal to the geographical location of the northern Gardar Drift where 76% of the variance in bottom velocity can be explained by changes in the volume transport and density of the Faroe Shetland Channel overflow. By contrast, Labrador Sea Water changes do not appear to play a significant role in the bottom flow over the Gardar Drift. Our findings support the assumption in the paleo literature that reconstructions of bottom water velocity at the Gardar Drift reflect past changes in the eastern Nordic Seas overflows. However, our results suggest that velocity changes downstream are not a simple metric for the strength of the overflow, rather overflow density plays the largest role.

Variability in the Northern North Atlantic and Arctic Oceans Across the Last Two Millennia: A Review

“…While overflows have received less attention than other large‐scale features of the North Atlantic circulation in the simulations of the past millennium, the ability to constrain overflow rates from proxy information, including sortable silt and magnetic particles (see section ), makes this a useful model diagnostic. In the BCM model, Langehaug et al () linked velocity changes along the Gardar Drift to the Faroe Shetland Channel overflow, thus supporting the use of ISOW reconstructions from the Gardar Drift as proxies for overflow properties. They also found, however, that velocity changes downstream are not a reliable metric for the strength of the overflow and that, instead, the density of overflow waters can be a better proxy.…”

A Review of the Role of the Atlantic Meridional Overturning Circulation in Atlantic Multidecadal Variability and Associated Climate Impacts

“…The multidecadal variability observed in the Iceland Scotland Overflow Water (ISOW) compared with the Gray et al () AMV reconstruction, adapted from Mjell et al (). At top, the detrended sortable silt (SS) data from core GS06‐144‐09MC‐D (thin gray line with three‐point smoothing in black), is a proxy for changes in the bottom water flow speed along the southward flow path of ISOW interpreted to reflect changes in the strength of ISOW (Langehaug et al, ; Mjell et al, ). The age model for the SS record uses published dates from Mjell et al () but is updated with new constraints on the core top age using the carbon isotope Suess effect (Irvali et al, in preparation/personal communication).…”

Relative timing of precipitation and ocean circulation changes in the western equatorial Atlantic over the last 45 ky

“…Cross-correlation has nevertheless been recently applied to climatic signals (Langehaug et al, 2016), including Pa/Th and δ 13 C Cw records from the last glacial (Henry et al, 2016). In the latter study, cross-correlation between marine records from 25 two deep Bermuda Rise cores and the NGRIP ice oxygen isotopic record was used to infer that deep Bermuda Rise each individual time series, and, therefore, also the relative dating error of one time series with respect to the other.…”

“…Although this simple method has been applied to climatic time series in previous studies (Langehaug et al, 2016;Henry et al, 2016), such results must be interpreted with caution, since the method has been designed for signals that are stationary in time and is, therefore, not suitable for climatic signals. …”