Deglacial to Holocene Ocean Temperatures in the Humboldt Current System as Indicated by Alkenone Paleothermometry

Abstract

The response of the Humboldt Current System to future global warming is uncertain. Here we reconstruct alkenone‐derived near‐surface temperatures from multiple cores along the Peruvian coast to infer the driving mechanisms of upwelling changes for the last 20 kyr. Our records show a deglacial warming consistent with Antarctic ice‐core temperatures and a Mid‐Holocene cooling, which, in combination with other paleoceanographic records, suggest a strengthening of upwelling conditions. This cooling, during the globally warm Mid‐Holocene, is consistent with an intensification of the Walker Circulation and the South Eastern Pacific Subtropical Anticyclone, indicative of La Niña‐like conditions in the Tropical Pacific. Surprisingly, oxygen contents in the subsurface increased and productivity was low during the Mid‐Holocene, which are at odds with La Niña‐like conditions. This suggests that the Humboldt Current System reacts in multiple ways to a warmer world and may even include a reversal in the present day subsurface deoxygenation.

Bottom-water deoxygenation at the Peruvian margin during the last deglaciation recorded by benthic foraminifera

“…6). Nevertheless, both Holocene records of cores 59-1 and 52-2 suggested a trend of increasing bottom-water oxygenation that is in accordance with recently published results from the region (Salvatteci et al, 2016(Salvatteci et al, , 2018Mollier-Vogel et al, 2019). Moreover, it is possible that bottom waters became more oxic after the late Holocene as reported for the shelf during the last 100-150 years (Cardich et al, 2019).…”

Bottom-water deoxygenation at the Peruvian Margin during the last deglaciation recorded by benthic foraminifera

“…Besides, large standard deviations observed in the northernmost core 59-1 raised questions about the applicability of the method for the Holocene (Figure 6). Never-the-less; both Holocene records of core 59-1 and 52-2, suggested a slight recovery of the OMZ that is in accordance with recently published results from the region (Salvatteci et al, 2016;Salvatteci et al, 2018;Mollier-Vogel et al, 2019). Since the records are not continuous, we cannot constrain changes in [O2]BW after the late Holocene.…”

Archaeological climate proxies and the complexities of reconstructing Holocene El Niño in coastal Peru

“…Both archaeological proxy-based EN reconstructions may be correct, reflecting the presence of a long-term climate divide at ∼12°S. The SST pattern of COA is consistent with multiple lines of evidence (16)(17)(18)(19)(20) for this divide. Hu et al (32) identified 7 COA events between 1979 and 2017.…”

“…The coast exhibits a significant climate divide at about 12°S (e.g., refs. [16][17][18][19][20], with coastal oceanographic and climate changes more pronounced to the north. During normal (non-EN) years, the Peru Current flows north along the Chilean and Peruvian coasts, bringing cool, deep, nutrient-rich water to the surface through intense upwelling; under these conditions, the thermocline is near the surface.…”