Seasonal fluctuations of temperature, salinity, nitrate, chlorophyll and primary production at station H3/M1 over 1989-1996 in Monterey Bay, California

Time series of temperature, salinity, nitrate, primary production and chlor ophyll over 1989-1996 at station H3/M1 in central Monterey Bay, CA, USA, ar e described, and an 'average year' is calculated for each parameter. Surfac e spatial data on temperature, salinity, chlorophyll and primary production from spring and fall 1993 also are presented. Surface water (0-5 m) was co ldest and saltiest in spring (similar to 10-11 degrees C; S = 33.4-33.8), w armed during summer (similar to 14 degrees C), remained warm but freshened in fall (S = 33.3-33.4), and cooled and freshened further in winter ( simil ar to 13 degrees C, S = 32.9-33.3). Nitrate time series show high concentra tions (10-20 mu M) present at the surface during spring and summer; low con centrations (< 1 mu M) occurred sporadically during fall and winter. High p rimary production values ( > 100 mg C m(-3) da(-1)) occurred in upper 20 m of the water column, while high chlorophyll ( > 3 mg m(-3)) extended to 25- 30 m. Phytoplankton blooms occurred as pulses of primary production and chl orophyll during spring, summer and occasionally in fall. Springtime spatial data show a surface 'plume' of cold, salty, low chlorophyll and low primar y production water extending N-S across the mouth of the Monterey Bay. The time-series station H3/M1 lies in the path of this plume. High chlorophyll and productivity values occur on the margins of the plume. Fall spatial dat a show temperatures and salinities warmer and fresher than spring while chl orophyll and primary production values were low. There was less spatial var iability in fall. A temperature/salinity time series for Monterey Bay from 1951 to 1991 (Kuo, 1991) shows similar seasonal patterns. However, the 1989 -1996 time series is warmer and fresher to at least 100 m, particularly dur ing non-upwelling seasons, and shows a later onset of upwelling. These diff erences are in accord with the 'regime shift' associated changes documented for the California Current by other workers. Long-term climatologies for n itrate, chlorophyll and primary production are not available for comparison with thr data presented in this paper. (C) 2000 Elsevier Science Ltd. All rights reserved.