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 chlorophyll over 1989–1996 at station H3/M1 in central Monterey Bay, CA, USA, are described, and an `average year’ is calculated for each parameter. Surface spatial data on temperature, salinity, chlorophyll and primary production from spring and fall 1993 also are presented. Surface water (0–5 m) was coldest and saltiest in spring (∼10–11°C; S=33.4–33.8), warmed during summer (∼14°C), remained warm but freshened in fall ( S=33.3–33.4), and cooled and freshened further in winter (∼13°C; S=32.9–33.3). Nitrate time series show high concentrations (10–20 μM) present at the surface during spring and summer; low concentrations (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 chlorophyll during spring, summer and occasionally in fall. Springtime spatial data show a surface `plume’ of cold, salty, low chlorophyll and low primary 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 data show temperatures and salinities warmer and fresher than spring while chlorophyll and primary production values were low. There was less spatial variability 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 during non-upwelling seasons, and shows a later onset of upwelling. These differences are in accord with the `regime shift’ associated changes documented for the California Current by other workers. Long-term climatologies for nitrate, chlorophyll and primary production are not available for comparison with the data presented in this paper.