Effect of analytical conditions in wavelength dispersive electron microprobe analysis on the measurement of strontium-to-calcium (Sr/Ca) ratios in otoliths of anadromous salmonids

The use of strontium-to-calcium (Sr/Ca) ratios in otoliths is becoming a standard method to describe life history type and the chronology of migrations between freshwater and seawater habitats in teleosts (e.g. Kalish, 1990; Radtke et al., 1990; Secor, 1992; Rieman et al., 1994; Radtke, 1995; Limburg, 1995; Tzeng et al. 1997; Volk et al., 2000; Zimmerman, 2000; Zimmerman and Reeves, 2000, 2002). This method provides critical information concerning the relationship and ecology of species exhibiting phenotypic variation in migratory behavior (Kalish, 1990; Secor, 1999). Methods and procedures, however, vary among laboratories because a standard method or protocol for measurement of Sr in otoliths does not exist. In this note, we examine the variations in analytical conditions in an effort to increase precision of Sr/Ca measurements. From these findings we argue that precision can be maximized with higher beam current (although there is specimen damage) than previously recommended by Gunn et al. (1992).

Solar-cycle modulations of ENSO: a possible source of climatic change

An association between long-term changes in the solar cycle and the frequency of El Niño events has been identified in historical records of El Niño and sunspot number. Although no known mechanism can explain the apparent relationship, the association is strong. A possible coupling between the sun and the ocean's mixed layer, involving ENSO, is worthy of further study.

Rapid δ18O and δ13C isotopic shifts in late Pleistocene marine varves on the California margin

Upper Pleistocene sediments on the continental slope off Northern California contain alternations of varves and bioturbation produced by fluctuations in intensity of the coastal upwelling system. Stable isotopic analyses of benthic Foraminifera across a particularly well developed varve/bioturbation sequence deposited ~26,000 years ago reveal rapid shifts of ~0.25‰ in δ18O and ~0.4‰ in δ13C. The δ18O shift occurs within a varved section. Based on varve counts, the isotopic change occurred in less than 100 years. Timing and magnitude of the shift coincide with similar shifts observed in almost all other high-resolution δ18O records that have been interpreted as primarily representing global in-volume fluctuations.

A pollen/dinoflagellate chronology for DSDP Site 480, Gulf of California

DSDP Site 480 in the Gulf of California represents a paleoclimatic record of great potential significance. Much of the 152-meter section is varved, which means that proxy records of climatic change can be analyzed with unusual precision on a variety of time scales. In this paper we present pollen and dinoflagellate evidence that suggests that the base of the section is much older than was previously thought. We propose a basal date of between 300,000 and 350,000 YBP.

Tropical and subtropical moisture and southerly displaced North Pacific storm track: factors in the growth of late Quaternary lakes in the Mojave Desert

Historical flood events produced lakes in the Mojave River watershed in southeastern California and represent climatic conditions similar to those in the late Quaternary when perennial lakes formed in the Mojave Desert. Historical lakes are related to tropical and subtropical sources of moisture and an extreme southward shift of storm tracks. It is suggested that this atmospheric pattern occurred frequently during earlier periods with perennial lakes in the Mojave River drainage basin.

The role of direct observation in predicting climatic change

The National Oceanic and Atmospheric Administration Center for Ocean Analysis and Prediction (COAP) in Monterey, California, has assembled information to suggest how NOAA's facilities for observing the ocean and atmosphere might be applied to studies of paleoclimate. This effort resulted, indirectly, in several projects that combine direct observations of the ocean/atmosphere system with studies of past climate of the Pacific region. This article considers concepts that link the two kinds of investigations. It defines the thesis that direct observation of systems that generate paleoclimatic information is the nexus upon which understanding of climatic variability begins and upon which prediction of climate and global change depends.

Geochemical evidence for enhanced upwelling and organic productivity during the late Quaternary on the continental margin of northern California

EXTRACT (SEE PDF FOR FULL ABSTRACT): Laminated sediments are preserved in upper Pleistocene sections of cores collected on the continental slope at water depths within the present oxygen-minimum zone from at least as far north as the Klamath River and as far south as Point Sur. Comparison of sediment components in the laminae with those delivered to sediment traps as pelagic marine "snow" show the dark/light lamination couplets are indeed annual (varves). ... The presence of carbon-, sulfur-, and metal-rich sediments, as well as lack of bioturbation, all support the theory that the oxygen-minimum zone in the northeastern Pacific Ocean was more intense - in fact, anoxic - during the late Pleistocene in response to greater coastal upwelling and higher organic productivity.

Centennial oscillation of the climatic crescendo during the last glacial maximum: evidence from Lake Estancia, central New Mexico

Sediments deposited in late Pleistocene Lake Estancia, central New Mexico, contain a paleoclimatic record that includes the last glacial maximum and deglacial episode. Stratigraphic reconstruction of an interval representing the highstand of the lake that occurred during the last glacial maximum reveals ~2000-, ~600-, and ~200-year oscillations in lake level and climate. Shifting position of the polar jetstream in response to expansion and contraction of the North American ice sheet may be partly responsible for the millenial-scale changes in Lake Estancia but probably does not explain the centennial-scale oscillations.

An 800-year paleoflood record from the Sacramento Valley, California [abstract]

EXTRACT (SEE PDF FOR FULL ABSTRACT): Four cores recovered from Little Packer Lake in Glenn County, California, have provided a paleoflood record for the past 800 years. ... The sequence of flood deposits in the top 2 meters of the record shows a reasonable agreement with the known history of floods during the past 150 years. At least three major flood events are indicated for AD 1400-1525, although these dates may have to be revised when more dates become available.

Can lake sediments provide a record of tropical storms? The case of Laguna de Juanacatlan, Jalisco, Mexico [abstract]

EXTRACT (SEE PDF FOR FULL ABSTRACT): Laguna de Juanacatlan is a small (15 hectare) lake in the State of Jalisco, Mexico. Its sediments are predominantly varved and thereby offer the potential of a high resolution paleoclimatic record.

Multiple-proxy lacustrine record of moisture transport over western North America from 24,000 to 12,000 YBP, Lake Estancia, New Mexico [abstract]

EXTRACT (SEE PDF FOR FULL ABSTRACT): Pluvial Lake Estancia in central New Mexico experienced large and rapid fluctuations in surface area and elevation during the build-up to and termination of the last glacial maximum (LGM). Due to continuous groundwater discharge, a minimum pool covering about 400 square kilometers was maintained in the central basin until about 12,000 years ago, ensuring a continuous depositional sequence even during low stands of the lake. ... The sensitive response to fluctuations in climate by several independent proxies at Estancia show that transport of Pacific moisture over western North America changed dramatically during the last Ice Age, perhaps comparable to the large and rapid changes in climate documented from high-latitude ice and North Atlantic marine sediments for the LCM and its transitions.

A rock-magnetic and geomagnetic secular variation record from late-Pleistocene Lake Estancia, New Mexico [abstract]

EXTRACT (SEE PDF FOR FULL ABSTRACT): Exposed sediments of Late Pleistocene Lake Estancia contain a high resolution record of regional climate variability for the period about 12,000 to 32,000 years. A detailed rock-magnetic study is being performed on this well-dated, well-preserved sedimentary sequence to determine how the magnetic signature of sediments responded to regional climate change.