Eastern tropical Pacific hydrologic changes during the past 27,000 years from D/H ratios in alkenones

Abstract

[1] The tropical Pacific plays a central role in the climate system by providing large diabatic heating that drives the global atmospheric circulation. Quantifying the role of the tropics in late Pleistocene climate change has been hampered by the paucity of paleoclimate records from this region and the lack of realistic transient climate model simulations covering this period. Here we present records of hydrogen isotope ratios (dD) of alkenones from the Panama Basin off the Colombian coast that document hydrologic changes in equatorial South America and the eastern tropical Pacific over the past 27,000 years (a) and the past 3 centuries in detail. Comparison of alkenone dD values with instrumental records of precipitation over the past $100 a suggests that dD can be used as a hydrologic proxy. On long timescales our records indicate reduced rainfall during the last glacial period that can be explained by a southward shift of the mean position of the Intertropical Convergence Zone and an associated reduction of Pacific moisture transport into Colombia. Precipitation increases at $17 ka in concert with sea surface temperature (SST) cooling in the North Atlantic and the eastern tropical Pacific. A regional coupled model, forced by negative SST anomalies in the Caribbean, simulates an intensification of northeasterly trade winds across Central America, increased evaporative cooling, and a band of increased rainfall in the northeastern tropical Pacific. These results are consistent with the alkenone SST and dD reconstructions that suggest increasing precipitation and SST cooling at the time of Heinrich event 1.

Effects of alkalinity and salinity at low and high light intensity on hydrogen isotope fractionation of long-chain alkenones produced by <i>Emiliania huxleyi</i>

“…For example, δD C 37 values measured on alkenones extracted from Mediterranean sapropel S5 show similar trends to δ 18 O measured on planktonic foraminifera and suggest a salinity decrease of 6 in the eastern Mediterranean at the onset of sapropel formation (van der Meer et al, 2007). δD C 37 values from Panama Basin sediments show changes in amount of runoff from the San Juan River, aligning well with instrumental data and even tracking glacial to interglacial changes in salinity (Pahnke et al, 2007). Salinity changes in the Agulhas Current system were also recorded by changes in δD C 37 values during glacial terminations I and II and from the last glacial maximum into the Holocene, which align with δ 18 O foram values from the same region (Simon et al, 2015;Petrick et al, 2015;Kasper et al, 2014).…”

Signatures of Tibetan Plateau heating on Indian summer monsoon rainfall variability

“…The regressions in (2) and (3) would then call for 212 mm/yr more rainfall than today. Moreover, at~6 ka, the eastern tropical Pacific Ocean was cooler than today by~1 C [e.g., Kienast et al, 2006;Koutavas et al, 2002Koutavas et al, , 2006Leduc et al, 2007Leduc et al, , 2010Pahnke et al, 2007]. If we assume a NINO4 index of -1 C, this could correspond to 17 mm/yr more rainfall early and late monsoon seasons than today, and the combination of a warmer Tibet by 5 C and a cooler NINO4 region by 1 C would lead tõ 230 mm, or~23%, more annual rainfall than today.…”

Impact of Earth’s orbit and freshwater fluxes on Holocene climate mean seasonal cycle and ENSO characteristics

“…We present the results of the t test showing both the 5 and 10% confidence level (dotted lines). This figure shows that the reduced SST warming rate induced by insolation changes during the autumn preceding the peak warming are statistically significant from control for 9.5 Table 2 Syntheses of the different studies used to infer the changes in temperature, precipitation and variability during early to midHolocene (Stott et al 2004;Shulmeister and Lees 1995;Turney et al 2004;Riedinger et al 2002;Koutavas et al 2006;Partin et al 2007;Benway et al 2006;Kienast et al 2006;Pahnke et al 2007;Koutavas et al 2002;Tudhope et al 2001;Rodbell 1999;Moy et al 2002;Haug et al 2001;Lea et al 2000 …”