Kachemak Bay Oceanographic Report, March-May 2026
Summary
This spring was cold! While air temperatures oscillated between colder than the 10th percentile for the season and normal, water temperatures were well below normal since last December, making this the longest, most intense cold snap since the beginning of this study in 2012. Chlorophyll concentrations were above the seasonal average in April, but dropped again to unusually low levels in May.
A complete set of up-to-date graphs can be found on this Google Drive: section plots and time sections (request access from martin.renner@noaa.gov).
Conditions
Air temperatures in Homer since the start of the year saw wild swings. Early January was unusually cold, early February was above normal, and early March was extremely cold for the season. Only by May had temperatures returned to the long-term average (Figure 1), which did not prevent a snow fall on 20 May. After an unusually dry March, May 2026 was unseasonally wet. Snow pack in the Kachemak Bay area in the 2025/26 winter was low, close to the 10th percentile. At times in April-May, snowpack was even tied with the record-low snow year 2015.
Hans, Kris and Paul conducted the in March and April KBL monthly surveys, Hans, Kris, and Martin were the crew for the May survey.
Physical oceanography
Temperature
Water temperatures during the most recent May survey ranged from a minimum of station 3.9 °C at station AlongBay-12 (70 m depth), in the inner bay, to a maximum of 6.8 °C at station 9-9 (1 m depth) off the Homer Spit. In March, and to a lesser degree in April, we found a vertically mixed and horizontally stratified water column in Kachemak Bay, with a transition zone near the Homer Spit (Figure 2 (a), top-left panel). By May, this pattern had completely reversed, showing strong vertical stratification, especially in the inner bay, and only moderate horizontal differences. Surface waters in the inner bay switched from colder than the outer bay to warmer between out April and May surveys.
Satellite sea surface temperature data showed that in contrast to inner Kachemak Bay, upper Cook Inlet remained colder than the lower inlet and the Gulf of Alaska (Figure 3). Almost all of Kachemak Bay was colder than normal throughout March to May (Figure 2), especially in April, large parts of the bay were over 1.8 standard deviations colder than average. The cold snap that started in December 2025 was evident through the entire water column. No other time since the beginning of this study in February 2012, had been this cold for this long (Figure 4, Figure 7). Surface waters of the Gulf of Alaska in May 2026, as shown by satellite data, were a global exception: only one other larger areas had temperature anomalies colder than -1 °C, whereas most of the world’s oceans were warmer than normal (Figure 5).
Salinity
Salinity values during the May survey ranged from 29.7 PSU at station 9-6 (1m depth) near Homer Spit to 31.6 PSU at station AlongBay-2 (112m depth) in the outer bay. Inner bay waters were fresher than outer bay waters in all three months (Figure 2). As with temperature, inner and out bay waters were mostly vertically mixed in March, but vertical stratification built up by April.
Compared to the long-term means, Kachemak Bay was fresher than seasonally expected in March and April, in some surface waters by over one standard deviation (Figure 2). In May, only inner bay surface waters were still fresher than normal, whereas outer bay and mid to deep waters were more saline than normal (Figure 2, @fix-TSprofile_T9, Figure 9).
Turbidity
Inner bay waters were more turbid than outer bay waters in all three months. In April and May, turbid waters extended from the inner bay into deep waters of the outer bay (Figure 2 (c), Figure 2 (f)). Compared to the long-term mean, a station off the Spit was unusually turbid.
Biological conditions
Phytoplankton
Chlorophyll concentrations were low throughout Kachemak Bay in March and were also low compared to the long-term mean. By April, things had changed substantially, as concentrations had increased throughout the study area and water column. Highest concentrations were found on the north end of Transect 4, off the Homer Bluff (Figure 2 (c)). Especially deep and mid waters had chlorophyll concentrations that were in places substantially above the long-term normal (above 2 standard deviations, Figure 2 (d), Figure 2 (e)). At the mid-bay station T9-6, full-column chlorophyll concentrations were above the mean (Figure 10). This April bloom had completely collapsed by the time of the May survey. While surface waters contained chlorophyll in elevated concentrations compared to deep water, all stations had less chlorophyll than expected from the long-term mean, reaching two standard deviations below the mean in some cases (Figure 2 (f) , Figure 2 (g)). Remarkably, while chlorophyll concentrations are expected to go up from April to May, they went down during this interval in 2026 (Figure 10).
Wildlife
Coinciding with the cold temperatures in the bay, an ivory gull, a rare species from the high arctic, was present in Homer Harbor during mid May.
Mailing list
Please email Martin at martin.renner@noaa.gov if you would like to be added to or removed from this mailing list.
Appendix
