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, deep water temperatures were well below normal since last December, making this the longest, most intense cold spell since the beginning of these routine oceanographic observations in 2012. Mid-bay chlorophyll concentrations were above the seasonal average in April, then dropped 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 were mostly well below normal since the start of the year, with a brief warmup in late January/early February. Early March was extremely cold for the season. Temperatures warmed close to the long-term mean in April and May (Figure 1), yet there was snowfall in Homer on 20 May. After an unusually dry March, May 2026 was unseasonably wet. Snow pack in the Kachemak Bay area in the 2025/26 winter was low with a peak near the 10th percentile. At times in April-May, snowpack at the Anchor River Divide station was close to the record-low snow year 2015 (Figure 2).
Kasitsna Bay Lab oceanographic surveys were conducted by Hans, Kris and Paul (March, April) and Hans, Kris, and Martin (May).
Physical oceanography
Temperature
Water temperatures during the most recent May survey ranged from a minimum of 3.9 °C at station AlongBay-12 (70 m depth), in the inner bay, to a maximum of 6.8 °C at station T9-9 (1 m depth) off the Homer Spit. In March the water column was mostly vertically mixed, with a transition zone near Homer Spit from warmer ocean to cooler bay waters (Figure 3 (a), top-left panel). A shallow, fresher and warmer surface layer developed in the inner bay in April, with the inner bay and northern parts of the outer bay remaining relatively cooler than waters in the rest of the outer bay. In May, strong vertical stratification was observed, with a very fresh surface layer in the inner bay that had switched to be warmer than the outer bay.
May 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 4). Almost all of Kachemak Bay was colder than normal throughout March to May (Figure 3), especially in April, when 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 bay waters been this cold for this long (Figure 5, Figure 8). Compared to bottom waters (Figure 8), surface waters, as measured by the KBNERR SWMP station, followed air temperatures (Figure 1) closely, albeit with a few days delay (Figure 7). Surface waters of the Gulf of Alaska and Bering Sea also remained colder than normal in May 2026, as shown by satellite data, in contrast to warmer than normal conditions across much of the North Pacific (Figure 6).
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, with surface freshening of inner bay waters in April that built up to strong vertical stratification by May (Figure 3). An interesting feature observed in March was the downward mixing of relatively fresh, cold water near the end of the Homer Spit, related to melting sea ice in that area (Figure 3 (a), Figure 3 (b)).
Compared to the long-term means, Kachemak Bay was more saline than seasonally expected in March and in upper parts of the water column also in April, reaching over one standard deviation in some places (Figure 3). In May, only inner bay surface waters were still more saline than normal, whereas outer bay and mid to deep waters were now fresher than normal (Figure 3, Figure 9, Figure 10). These patterns are consistent with the prolonged winter cold, with spring increases in freshwater inputs to the bay coming later than normal.
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 3 (c), Figure 3 (f)). Areas of higher surface turbidity were found in some areas of transient fresher surface water plumes,
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 at 10-20 m depth on the north end of Transect 4, in the outer bay off Bluff Point (Figure 3 (c)). Some deep and mid waters had chlorophyll concentrations over two standard deviations above the long-term normal (Figure 3 (d), Figure 3 (e)). At the mid-bay station T9-6, chlorophyll concentrations integrated across the water column were above the mean (Figure 11). Surprisingly, chlorophyll concentrations were lower in all locations during the May survey, as compared to April. While chlorophyll concentrations in surface waters were higher than in deep waters, all stations had less chlorophyll than expected from the long-term mean, reaching two standard deviations below the mean in some cases (Figure 3 (f), Figure 3 (g)).
Wildlife
An ivory gull, a rare species from the high Arctic, was present in Homer Harbor during mid May. Few marine mammals were observed during the March, April and May surveys this year.
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
