# Relatively warm deep-water formation persisted in the Last Glacial Maximum

## TL;DR

During the Last Glacial Maximum, the deep Northwest Atlantic was only slightly colder than today, indicating ongoing formation of relatively warm deep water.

## Contribution

The study provides new temperature and isotopic data from the deep Northwest Atlantic during the Last Glacial Maximum.

## Key findings

- The deep Northwest Atlantic was approximately 0–2 °C during the Last Glacial Maximum.
- Seawater δ18O was 0.3 ± 0.1‰ higher, traced back to the surface subtropics.
- Results suggest sustained production of relatively warm and salty North Atlantic Deep Water during the Last Glacial Maximum.

## Abstract

The Last Glacial Maximum (19–23 thousand years ago) was characterized by low greenhouse gas concentrations and continental ice sheets that covered large parts of North America and Europe1. Glacial climate was therefore very different, with colder global mean temperatures and an increased Equator-to-pole temperature gradient, probably resulting in stronger westerlies2. However, the state of the deep North Atlantic Ocean under these glacial climate forcings remains uncertain3–6, particularly owing to the rarity of deep-ocean temperature and salinity constraints. Here we show that the temperature of the glacial deep (>1.5 km) Northwest Atlantic was approximately 0–2 °C (only 1.8 ± 0.5 °C (2 s.e.) colder than today), and, after accounting for the whole-ocean change, seawater δ18O was 0.3 ± 0.1‰ (2 s.e.) higher and can be traced back to the surface subtropics via the subpolar Northeast Atlantic and Nordic Seas. Together, our hydrographic data reveal the thermal and isotopic structure of the deep Northwest Atlantic and suggest sustained production of relatively warm and probably salty North Atlantic Deep Water during the Last Glacial Maximum. Furthermore, our results provide updated constraints for benchmarking Earth system models used to project future climate change.

During the Last Glacial Maximum, the deep Northwest Atlantic was only about 2 °C colder than today, suggesting sustained production of relatively warm North Atlantic Deep Water during the Last Glacial Maximum.