Records of past climate can inform us on the natural range and mechanisms of climate change. In the arid Pacific southwestern United States (PSW), which includes southern California, there exist a variety of Holocene records that can be used to infer past winter conditions (moisture and/or temperature). Holocene records of summer climate, however, are rare from the PSW. In the future, climate changes due to anthropogenic forcing are expected to increase the severity of drought in the already water stressed PSW. Hot droughts are of considerable concern as summer temperatures rise. As a result, understanding how summer conditions changed in the past is critical to understanding future predictions under varied climate forcings. Here, we present a c. 10.9 kcal BP δ 18 O (calcite) record from Lake Elsinore, California, interpreted to reflect δ 18 O (lake water) values as controlled by over-water evaporation from summer-to-early fall. Our results reveal three millennial scale intervals: (1) the highly evaporative Early Holocene (10.55-6.65 kcal BP), (2) the less evaporative Mid-Holocene (6.65-2.65 kcal BP); and (3) the evaporative Late Holocene (2.65-0.55 kcal BP). These results are coupled with an inferred winter precipitation runoff (sand content) record from Kirby et al. (2010). Using these data together, we estimate the duration and severity of centennial-scale Holocene droughts and pluvials (e.g., high δ 18 O (calcite) values plus low sand content = drought and vice versa). Furthermore, the coupled δ 18 O (calcite) and sand data provide a generalized Holocene lake level history. The most severe, long-lasting droughts (i.e., maximum summer-to-early fall evaporation and minimum winter precipitation runoff) occur in the Early Holocene. Fewer, less severe, and shorter duration droughts occurred during the Mid-Holocene as pluvials became more common. Droughts return with less severity and duration in the Late Holocene. Notably, the Little Ice Age is characterized as the wettest period during the Late Holocene.

No abstract

ABSTRACT. New photoelectric photometry and new times of maximum light are reported for the 8 Scuti-type star VZ Cancri. Times of maximum light available for the last five decades have been studied. The times of maximum from the last decade, however, indicate that the period has not been steadily increasing as believed until now. To allow for this discrepancy several interpretations of the O-C diagram are discussed. However, the scatter in the (O-C) residuals is large and it is difficult to favor a case between a sloping linear fit and a sinusoidal fit. The former indicates that the main period needs to be revised and a predicted value of 0.17836365 days is obtained. The later suggests the presence of an unseen companion whose nature and implications are briefly discussed. In either case it can be concluded that VZ Cnc is not undergoing any secular period variation. Other possibilities like abrupt period changes and long-term effects of nonlinear combinations of short frequencies are discussed but found unrealistic.

Paleoperspectives of climate provide important information for understanding future climate, particularly in arid regions such as California, where water availability is uncertain from year to year. Here, we present a record from Barley Lake, California, focusing on the interval spanning the Younger Dryas (YD) to the early Holocene (EH), a period of acute and rapid global climate change. Twelve radiocarbon dates constrain the timing between 12.9 and 8.1 ka. We combine a variety of sediment analyses to infer changes in lake productivity, relative lake level, and runoff dynamics. In general, the lake is characterized by two states separated by a <200-year transition: (1) a variably deep, lower-productivity YD lake; and (2) a two-part variably shallow, higher-productivity EH lake. Inferred EH winter-precipitation runoff reveals dynamic multidecadal-to-centennial-scale variability, in agreement with the EH lake-level data. The Barley Lake archive captures both hemispheric and regional signals of climate change across the transition, suggesting a role for both ocean-atmosphere and insolation forcing. Our paleoperspective emphasizes California's sensitivity to climate change and how that change can generate abrupt shifts in limnological regimes.

Abstract. Observations obtained in 1995-1996 of the Be star OT Geminorum are reported and show that in october 1995 the star reached a very active phase with large variations around a bright plateau, a phase of activity we have also distinguished in previous observations dating from 1960.The time scales involved are discussed and suggest that the violent variations of the activity propagate very quickly on the whole surface of the star or on a huge portion of it. No likely pulsation periods were found.The assumption that the detected activity is due to the effects of an hypothetical companion leads to conclude that such companion could not be detected by the present interferometric techniques.