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

Abstract

International audienceClimate 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 the present-day 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

Benthic nitrogen cycling traversing the Peruvian oxygen minimum zone

“…The model was run to steady-state (∂C/∂t = 0), although we are aware that the shelf is a more transient environment than the deeper slope settings. For example, an increase in POC accumulation rates began around 1820 AD (Gutiérrez et al, 2009) and the shelf bottom waters were renewed and ventilated in 1993 and 1997/98 in response to El Niño events (Gutiérrez et al, 2008). Nonetheless, we argue that (i) the relatively slow change in solid accumulation rates beginning ca.…”

Nutrient utilisation and weathering inputs in the Peruvian upwelling region since the Little Ice Age

“…AD 1400 and 1850 (Lamb, 1965;Grove, 2001). During that time a weakening of the Walker circulation (Conroy et al, 2008), a reduced influence of the South Pacific subtropical high (SPSH) along the Peruvian margin Gutiérrez et al, 2009;Salvatteci et al, 2014a), and a southward shift of the mean position of the Intertropical Convergence Zone (ITCZ) and the associated precipitation belt compared to today (Sachs et al, 2009) caused pronounced changes in rainfall patterns in the tropics. El Niño-like warmer conditions in the eastern South Pacific were accompanied by an intensified South American summer monsoon (Bird et al, 2011), resulting in ∼ 10 % higher precipitation in northeastern Peru (∼ 5 • S; Rabatel et al, 2008) and up to 20-30 % higher precipitation in the Bolivian Andes (∼ 16 • S; Reuter et al, 2009).…”

“…On the one hand this caused growth and extension of the Andean glaciers (Vuille et al, 2008) and on the other it enabled human settlements in the presently hyperarid southern Peruvian Andes (Unkel et al, 2007). In the upwelling areas off Peru and the western South American shelf regions, the main consequence of these climatic conditions during the LIA was a deepening of the nutricline and a strongly diminished biological productivity (Vargas et al, 2007;Sifeddine et al, 2008;Valdés et al, 2008;Gutiérrez et al, 2009).…”

Insight on population structure of the Chilean jack mackerel (Trachurus murphyi)

“…This was obvious in the late 1990s to early 2000s when all the subpopulations decreased synchronously, from Peru and Chile to New Zealand. In the South Pacific Ocean, the strong climatic signals at interannual (e.g., El Niño southern oscillation: Barber and Chavez 1983), decadal (Chavez et al 2003) and centennial (Sifeddine et al 2008;Gutiérrez et al 2009) scales are known to have a strong impact on the whole ecosystem, ergo on fish stocks. In this highly dynamic context (see Chavez et al 2008), T. murphyi has developed a strategy of a few successful recruitments (in average 1 every 5 years) that lead the whole population and consequently its exploitation (Konchina and Pavlov 1999).…”