Recent increase in surface-water stability during warming off California as recorded in marine sediments

Journal Article · Mon Nov 01 04:00:00 EST 1999 · Geology

DOI:https://doi.org/10.1130/0091-7613(1999)027<1019:RIISWS>2.3.CO;2· OSTI ID:20003865

Weinheimer, A L; Kennett, J P; Cayan, D R

Warming of surface waters in the California Current since the 1950s has coincided with a significant decline in zooplankton volume. This has been attributed to reduced upwelling of nutrient-rich waters caused by increased thermal stratification across the thermocline. Proxy microfossil evidence preserved in the Santa Barbara Basin suggests that stability increased early in the 1900s, intensified after the early 1940s, and became well established by 1960. Accumulation of upwelled radiolarians in the basin has steadily declined since 1900, while oxygen isotopes in surface-dwelling planktonic foraminifera reflect increasing surface temperatures. Comparison of the {delta}{sup 18}O records between surface and thermocline-dwelling planktonic foraminifera reveals that the temperature difference between surface and thermocline water has increased during the twentieth century. Instrumental records of surface and thermocline temperatures, monitored since 1950, support these results. This evidence suggests that relaxation of North Pacific anticyclonic gyre circulation deepened isopycnics, causing onshore movement of warmer, less saline waters and reduced upwelling of cool, nutrient-rich waters.

• Research Organization: Univ. of California, San Diego, La Jolla, CA (US)
• Sponsoring Organization: US Department of Energy
• OSTI ID: 20003865
• Journal Information: Geology, Journal Name: Geology Journal Issue: 11 Vol. 27; ISSN 0091-7613; ISSN GLGYBA
• Country of Publication: United States
• Language: English

Related Subjects

58 GEOSCIENCES
AMBIENT TEMPERATURE
BIOLOGICAL INDICATORS
CALIFORNIA
COASTAL WATERS