Fig. 3: Hydrographic structure of the Northwest Atlantic during the mid-to-late Holocene and LGM.
From: Relatively warm deep-water formation persisted in the Last Glacial Maximum
a–f, Vertical temperature (a,d) and δ18Osw (b,e) profiles, and temperature versus salinity (T/S) cross-plots (c,f) for the mid-to-late Holocene (MH; a–c) and the LGM (d–f). In b and f, the use of grey versus black axis labels denotes weaker (grey) versus more robust (black) proxy reconstruction. The filled coloured symbols in a, b, d and e represent the mean value for each depth (individual and mean monospecific temperature data and are shown in Extended Data Fig. 4), and associated errors bars are ±2 s.e. (Methods). All δ18Osw data are reported relative to the Standard Mean Ocean Water (SMOW) scale. The dashed black lines are locally weighted scatterplot smoothing lines (smoothing span, 1) through all foraminiferal temperature data from this study. The grey line and ribbon in a and b, respectively, denote the modern temperature from WOA237 and the δ18Osw structure of the Northwest Atlantic (in the absence of modern in situ δ18Osw measurements, a range of δ18Osw was derived using salinity data from WOA23 (ref. 8) and modern salinity–δ18Osw relationships (NADW, North Atlantic (NATL) and LSW25)). The dotted best fit line in d shows the shift to warmer temperatures, most probably owing to the influence of a deeper glacial subtropical gyre at Blake Outer Ridge14. Ostracod temperature data are derived from published benthic ostracod shell Mg/Ca ratios22,23,24. The glacial δ18Osw estimate at approximately 4.5 km is derived using published ostracod Mg/Ca temperature data and nearby published benthic foraminiferal δ18O data45,46. Symbol colours in c and f correspond to core water depth and associated errors are ±1 s.e. (Methods). Isopycnals of σ2 were calculated using modern temperature and salinity measurements from the Global Ocean Data Analysis Project (GLODAP, v2.2022)47 and the Gibbs seawater Oceanographic Toolbox (TEOS-10 standard)48. North Atlantic (20–60° N, 0–80° W) GLODAP (v2.2022) temperature and salinity measurements are also plotted as smaller coloured circles and coloured according to water depth in c. To aid comparison, c and f are offset by 1.1 PSU to account for the LGM–Holocene whole-ocean salinity difference, derived from the change in global sea level. gNADW, glacial North Atlantic Deep Water; gNABW, glacial North Atlantic Bottom Water.
