Tracking Thermal Anomalies
The Bodega Marine Laboratory has been tracking local sea temperature since 1956. This effort began with daily manual measurements, which continued until an automated system was deployed in 1988, sampling the inflowing seawater at the BML pumphouse. When the intake system is unavailable, data from a temperature logger at the seaward end of the intake pipe are used to fill gaps. During recent construction on the pumphouse, real-time SOFAR buoy measurements have been used to extend record.
The figure below provides an up-to-date visual of seawater temperatures at BML from 2025 and 2026 and a comparison with the long-term high-frequency record beginning in 1988. Daily observations are plotted using daily means from hourly medians to reduce the influence of outliers. The long-term average and the 90th and 10th percentiles are calculated using observations within five calendar days on either side of each day of the year. These seasonal reference curves are then smoothed using a circular 31-day moving mean to reduce short-term variability while preserving the annual cycle. Temperatures above the 90th percentile represent unusually warm waters, while temperatures below the 10th percentile represent unusually cool conditions. Anomalously high temperatures lasting for 5 or more days are demarcated as marine heat wave (MHW) events.
Anomalously warm waters were observed in September and October 2025, as well as during the following winter (particularly February 2026), consistent with warm water anomalies at shorelines elsewhere in California. However, with the onset of upwelling in March, temperatures have been typical most of the time. Exceptions occurred during weak winds in April and June. Quite likely we will see more warm water anomalies during the fall and winter as seasonal upwelling winds weaken.
To date, the highest daily mean sea temperature recorded at BML was 18.79 °C on August 7, 2022, and the lowest was 7.60 °C on December 23, 1990.
Persistent, anomalously warm ocean temperatures, known as marine heat waves, place substantial growing stress on coastal ecosystems. Rapidly changing conditions can outpace the ability for marine organisms to adapt, relocate, or recover. As a result, fisheries may notice a decline in catch, sheltered coastal waters (i.e., bays, estuaries, lagoons) may become more vulnerable to harmful algal blooms (HAB), and marine mammal strandings may increase as prey availability decreases. Widespread coral bleaching and entire loss of kelp forest ecosystems may also occur, which, as foundation species, provide essential habitat for many marine organisms to live and thrive.
As of August 2026, El Niño is strengthening, and NOAA expects it to intensify throughout the remainder of the year. BML will continue to monitor local sea temperatures to assess the impact of this event on this region's coastal waters.