El Niño evolution during the Holocene revealed by a biomarker rain gauge in the Galápagos Islands

Abstract

International audienceThe El Niño-Southern Oscillation (ENSO) represents the largest perturbation to the climate system on an inter-annual time scale, but its evolution since the end of the last ice age remains debated due to the lack of unambiguous ENSO records lasting longer than a few centuries. Changes in the concentration and hydrogen isotope ratio of lipids produced by the green alga Botryococcus braunii, which blooms during El Niño rains in the Galápagos Islands, indicate that the early Holocene (9200–5600 yr BP) was characterized by alternating extremes in the intensity and/or frequency of El Niño events that lasted a century or more. Our data from the core of the ENSO region thus calls into question earlier studies that reported a lack of El Niño activity in the early Holocene. In agreement with other proxy evidence from the tropical Pacific, the mid-Holocene (5600–3500 yr BP) was a time of consistently weak El Niño activity, as were the Early Middle Ages (∼1000–1500 yr BP). El Niño activity was moderate to high during the remainder of the last 3500 years. Periods of strong or frequent El Niño tended to occur during peaks in solar activity and during extended droughts in the United States Great Plains linked to La Niña. These changing modes of ENSO activity at millennial and multi-centennial timescales may have been caused by variations in the seasonal receipts of solar radiation associated with the precession of the equinoxes and/or changes in solar activity, respectively

Holocene sea level and climate variability on the Great Barrier Reef, Australia

“…5c). Our combined coral luminescence record is in agreement with previous climate reconstructions indicating reduced frequency of ENSO between ~5500 and 3500 y BP in the eastern Pacific Galapagos Islands (Zhang et al, 2014), central Pacific Line Islands (Cobb et al, 2013), and Kiritimati Island . Reduced intensity and variability of luminescent signals have also been reported for a series of fossil corals (~6000 y BP) from Magnetic Island (~40 km south of GPI), which is also influenced by Burdekin River discharge .…”

“…Massive fossil corals offer the ability to conduct high-resolution sampling at sub-annular scales (Cobb et al, 2013, Zhang et al, 2014; however, finding a continuous temporal sequence of samples across millennia is difficult, and the preservation state of the corals greatly affects geochemical signal reliability Gagan, 2003, McGregor andAbram, 2008). At nearshore locations on the GBR, measured and visually assessed annual coral UV luminescence signals have been shown to reliably record river flow and rainfall variability associated with both ENSO …”

“…increased terrestrial input) and reduced Sr/Ca seasonal SST range all represent a wetter and warmer phase on the GBR at~4600 yBP, reminiscent of modern La Niña like conditions. Clearly more Holocene 'windows' derived from both coral luminescence and geochemical proxy reconstructions are needed before a complete picture of ENSO variability can be assessed on the GBR throughout the Holocene, however data from elsewhere in Australia and in the wider Pacific generally supports reduced ENSO variability and strength during the mid-Holocene , Rodo and Rodriguez-Arias, 2004, Chiang et al, 2009, Carré et al, 2012, Cobb et al, 2013, Zhang et al, 2014, Emile-geay et al, 2016.…”

“…, Xu et al, 2010 and changes in the frequency and/or strength of ENSO events (e.g. Woodroffe et al, 2003, McGregor and Gagan, 2004, Conroy et al, 2008, Cobb et al, 2013, Zhang et al, 2014 will differentially effect coral reefs across the Indo-Pacific.…”

Interplay of community dynamics, temperature, and productivity on the hydrogen isotope signatures of lipid biomarkers

“…The hydrogen isotopic composition of lipids produced by cyanobacteria and eukaryotic algae is well correlated with those of source water in laboratory and field settings (Sauer et al, 2001;Huang et al, 2004;Englebrecht and Sachs, 2005;Zhang and Sachs, 2007;Sachse et al, 2012) and is stable under near-surface temperatures and pressures for carbon-bound hydrogen (Sessions et al, 2004;Schimmelmann et al, 2006). Hydrogen isotopes of biomarkers from eukaryotic algae have been successfully applied to infer changes in past climate using sediment cores from diverse lakes (Huang et al, 2002;Sachs et al, 2009;Smittenberg et al, 2011;Atwood and Sachs, 2014;Zhang et al, 2014;Nelson and Sachs, 2016;Richey and Sachs, 2016;Randlett et al, 2017) and marine settings (Pahnke et al, 2007;van der Meer et al, 2007van der Meer et al, , 2008Leduc et al, 2013;Vasiliev et al, 2013Vasiliev et al, , 2017Kasper et al, 2014).…”