Intermittent existence of a southern Californian upwelling cell during submillennial climate change of the last 60 kyr

Abstract

[1] Application of a high-resolution multiproxy approach to a sedimentary section drilled at Ocean Drilling Program Site 1017, located under a highly active upwelling cell off Point Conception, California, provides clear evidence for surface ocean productivity shifts on submillennial timescales during the last 60 kyr. The proxies include bulk-sediment major and minor elements, organic carbon and carbonate concentrations, d 15 N, and planktonic foraminiferal species assemblage and carbon isotope determinations. The collective results demonstrate that marine productivity in this area was not simply linearly related to cold and warm cycles except during the millennial-scale climate oscillations of marine isotope stage (MIS) 3. During that interval, the upwelling cell and resulting high productivity were active during warm interstadial events and were largely inactive during cool stadial events. However, the Last Glacial Maximum was also relatively productive. Productivity increased dramatically during the Bølling warm interval, while the Å llerød and Younger Dryas were much less productive. High coccolithophorid abundance commenced during the earliest Holocene after 10 ka. The complexity of the productivity response was probably related to interplay between local winds, as well as California Undercurrent strength.

Post-glacial redistribution and shifts in productivity of giant kelp forests

“…Analysis of southern California kelp canopy area and biomass records from 1968 to 2002 reveals predictably higher biomass density during periods of high productivity potential (La Niñ a) versus low productivity potential (El Niñ o; figure 3a), presumably owing to nutrient deficiency during El Niñ o events (Zimmerman & Robertson 1985;Tegner et al 1997). Furthermore, recently published palaeooceanographic records (Hendy et al 2002(Hendy et al , 2004Friddell et al 2003) for the last 20 000 years reveal an abrupt shift in late Quaternary oceanographic productivity potential, from cold unproductive conditions at the LGM to warmer, more productive conditions from 15 600 yr BP to present (figure 3b). The low productivity potential of the LGM may be analogous to long-term El Niñ o conditions (Ortiz et al 2004).…”

“…Thus, to estimate late Quaternary changes in giant kelp productivity potential we chose proxies for three environmental variables: sea surface temperature (SST), presence of nutrient-rich sub-photic water (d 15 N) and surface water productivity (%C org ) from the varved sediments of the Santa Barbara Basin, one of the best-known regional records of late Quaternary climate change (Kennett & Ingram 1995). Data from two well-studied sediment cores in the Santa Barbara Channel region, Hole 1017E and Hole JPC76, were used to reconstruct periods of low or high productivity potential since the LGM (SST: Friddell et al 2003;Hendy et al 2004;d 15 N: Hendy et al 2004;%C org : Hendy et al 2002). These proxies provided independent measures of relative changes in temperature, nutrient delivery and productivity, three processes that are highly coupled at daily to decadal scales but may be decoupled at centennial to millenial and longer time scales.…”

Abrupt climate change: An alternative view

“…That an equivalent degree of high frequency variability exists in both records is evident; whether the oscillations actually correspond as the dashed lines indicate, is much less obvious. Note that Hendy et al (2004) invoke local wind and ocean circulation effects to rationalize the Santa Barbara record. Stuiver and Grootes (2000) as used by Peterson et al (2000).…”

Increase in water column denitrification during the last deglaciation: the influence of oxygen demand in the eastern equatorial Pacific

“…Siliciclastics are, therefore, the main sedimentary fraction diluting the organic carbon contents of the sediment. Normalization of organic carbon to the concentration of a refractory element (as Titanium (Ti), or Aluminium (Al) found in the silicoclastic sediment may then correct for variable dilution effects and has the potential to give a good estimate of organic material input to the sediment over time (see Calvert and Pedersen, 2007;Hendy et al, 2004;. We used the Ti content, commonly and easily measured by XRF core-scanning, as an estimate of the terrigeneous fraction.…”