Solar forcing of Gulf of California climate during the past 2000 yr suggested by diatoms and silicoflagellates

Abstract

High-resolution records of the past 2000 yr are compared in a north-south transect (28°N to 24°N) of three cores from the eastern slopes of the Guaymas, Carmen, and Pescadero Basins of the Gulf of California (hereafter referred to as the "Gulf"). Evenly-spaced samples from the varved sediments in each core allow sample resolution ranging from ∼ 16 to ∼ 37 yr.Diatoms and silicoflagellates capture the seasonal variation between a late fall to early spring period of high biosiliceous productivity, that is driven by northwest winds, and a summer period of warmer, more stratified waters during which these winds slacken and/or reverse direction (monsoonal flow). As these winds decrease, tropical waters enter the Gulf and spread northward. Individual samples represent a composite of 7 to 23 yr of deposition and are assumed to record the relative dominance of the winter vs. summer floral components.Intervals of enhanced summer incursion of tropical waters, alternating with periods of increased late fall to early spring biosiliceous productivity are recorded in all three cores. Regularly spaced cycles (∼ 100 yr duration) of Octactis pulchra, a silicoflagellate proxy for lower SST and high productivity, and Azpeitia nodulifera, a tropical diatom, occur between ∼ A.D. 400 and ∼ 1700 in the more nearshore Carmen Basin core, NH01-21 (26.3°N), suggesting a possible solar influence on coastal upwelling.Cores BAM80 E-17 (27.9°N) and NH01-26 (24.3°N) contain longer-duration cycles of diatoms and silicoflagellates. The early part of Medieval Climate Anomaly (∼ A.D. 900 to 1200) is characterized by two periods of reduced productivity (warmer SST) with an intervening high productivity (cool) interval centered at ∼ A.D. 1050. Reduced productivity and higher SST also characterize the record of the last ∼ 100 to 200 yr in these cores. Solar variability appears to be driving productivity cycles, as intervals of increased radiocarbon production (sunspot minima) correlate with intervals of enhanced productivity. It is proposed that increased winter cooling of the atmosphere above southwest U.S. during sunspot minima causes intensification of the northwest winds that blow down the Gulf during the late fall to early spring, leading to intensified overturn of surface waters and enhanced productivity.A new silicoflagellate species, Dictyocha franshepardii Bukry, is described and illustrated.

El Niño–Southern Oscillation variability from the Late Cretaceous Marca Shale of California

“…3), may be characteristic of lower-frequency changes in ENSO (Enfi eld and Cid, 1991;Allan, 2000). On the other hand, these periods are close to the 11 yr Schwabe solar cycle, and decadal periodicities in Holocene-age Gulf of California sediments have also been linked to solar variability (Pike and Kemp, 1997) as have lower-frequency centennial-scale productivity cycles (Barron and Bukry, 2007). Following Pike and Kemp (1997), it may be that the Marca decadal periodicity denotes a response to a larger North Pacifi c circulation pattern rather than the more localized on June 3, 2015 geology.gsapubs.org Downloaded from signals of upwelling and monsoonal circulation that control lamina thickness.…”

Holocene landscape response to seasonality of storms in the Mojave Desert

“…Barron et al (2010), however, suggest that Santa Barbara basin SSTs were cooler between wAD 800 and 1350 and generally warmer between wAD 1400 and 1800 based on diatom and silicoflagellate assemblages. In contrast, Gulf of California records indicate cool SST and probable weakening of the North American monsoon during the wet interval of the MWP and much of the LIA (Barron and Bukry, 2007). (Barron et al, 2005).…”

“…6) as revealed by microfauna proxy data is striking (Barron et al, 2005;Barron and Bukry, 2007). Tropical diatoms and silicoflagellates interpreted as indicating warm SST are especially abundant during the Younger Dryas, but persist to w11 ka and are also present during the Bølling-Allerö d. During much of the early and middle Holocene between w11 and w6.2 ka, these tropical phytoplankton are absent from the central Gulf of California, implying cooler SST.…”

Precipitation variations of Longxi, northeast margin of Tibetan Plateau since AD 960 and their relationship with solar activity

“…Numerous studies show that solar activity is the main force that drives regional climate changes in the Holocene (Kilian et al, 1995;Stuiver et al, 1997;van Geel et al, 1999;Yu and Ito, 1999;Crowley, 2000;Hong et al, 2000;Perry and Hsu, 2000;Bond et al, 2001;Hodell et al, 2001;Neff et al, 2001;Speranza et al, 2002;Fleitmann et al, 2003;Frisia et al, 2003; Hu et al, 2003;Magny, 2004;Kilcik, 2005;Ogurtsov et al, 2005;Wang et al, 2005;Xu et al, 2006;Barron and Bukry, 2007;Haltia-Hovi et al, 2007;Rodolfo Rigozo et al, 2007). The synchronous variations of the precipitation of Longxi and the Northern Hemisphere temperature on multidecadal to centennial scales may be ascribed to the same control of solar activity.…”