Rapid reorganization in ocean biogeochemistry off Peru towards the end of the Little Ice Age

Abstract

Abstract. Climate and ocean ecosystem variability has been well recognized during the twentieth century but it is unclear if modern ocean biogeochemistry is susceptible to the large, abrupt shifts that characterized the Late Quaternary. Time series from marine sediments off Peru show an abrupt centennial-scale biogeochemical regime shift in the early nineteenth century, of much greater magnitude and duration than present day multi-decadal variability. A rapid expansion of the subsurface nutrient-rich, oxygen-depleted waters resulted in higher biological productivity, including pelagic fish. The shift was likely driven by a northward migration of the Intertropical Convergence Zone and the South Pacific Subtropical High to their present day locations, coupled with a strengthening of Walker circulation, towards the end of the Little Ice Age. These findings reveal the potential for large reorganizations in tropical Pacific climate with immediate effects on ocean biogeochemical cycling and ecosystem structure.

Climate change and marine ecosystems

“…As the polar ice caps expanded during the LIA, the mean position of the ITCZ was pushed southward of its present location (1, 2), shutting down the Walker circulation in the Pacific, one of the drivers of increased productivity off the coast of Peru. The abundant concentrations of small pelagic fish that in the present day make Peru the most productive region in the world in terms of fish (3) were hardly evident in sediment cores during the LIA but returned dramatically when conditions warmed (1). A similar migration of the ITCZ occurs seasonally when during the boreal winter the mean position is found 5-10°farther south than during boreal summer.…”

“…By looking to the past we know that climate-driven phenomena have resulted in large changes to marine ecosystems; dramatic shifts in the abundance of fish off the coast of Peru occurred at the end of the Little Ice Age (LIA) (1). These shifts were linked to a southward migration in the mean position of the InterTropical Convergence Zone (ITCZ).…”

Effect of the Little Ice Age on Climate and Vegetation Recorded by n-Alkanes and Glycerol Dialkyl Glycerol Tetraether Proxies

“…Today, the iontertropical convergence zone (ITCZ) migration and southern oscillation (SO) [52] significantly influence the climate in South America. During the LIA climate shifts in the northern Hemisphere continents led to changes in climate in the whole world, including the ITCZ which due winds strengthening, shifted southward and low latitude continental areas became more arid [6]. In such conditions, other current of air masses were affected, diversifying the climate changes on a global level [53,6].…”

“…During the LIA climate shifts in the northern Hemisphere continents led to changes in climate in the whole world, including the ITCZ which due winds strengthening, shifted southward and low latitude continental areas became more arid [6]. In such conditions, other current of air masses were affected, diversifying the climate changes on a global level [53,6]. Thus, although studies of the effects of these climate shifts in South America remain limited, they seem to be linked to regional atmospheric factors, which may have contributed to anti-correlated findings in South America [54].…”

“…Most studies have focused on the northern hemisphere [3][4][5], and there are few studies demonstrating the occurrence of the event in the southern hemisphere. For instance, in South America [6,7], advance in glaciers in the Andes was demonstrated [8], as well as aridity in the lowlands of Argentina [9] and Venezuela [8], and there is evidence from mountain glaciers suggesting increasing glaciation in Patagonia [10]. In Brazil, some studies have demonstrated change in vegetation composition during the LIA and sea level regression in northeastern and southeastern Brazil [11][12][13].…”