Monthly Oceanographic Kachemak Bay Report, December 2025
Summary
After a month of unseasonably cold, dry weather with northeasterly winds and ice in shallow waters, little sign of vertical ocean stratification remained. Differences remained between a colder and fresher inner, and a warmer, saltier outer bay. Throughout the water column, temperatures were below the long-term mean, in parts by over 1.2 standard deviations (SD). All but deep waters in the inner bay were 0-1 SD fresher than normal.
Conditions
Weather in the month leading up to this survey was unusually cold (Figure 1) and dry, with winds generally blowing from the northeast. Beluga Lake was frozen but there was virtually no snow on the ground at sea-level. Mud Bay was filled with ice and Homer Harbor was impassable for small vessels due to the amount of ice. Hans, Martin, and Paul conducted the KBL monthly survey on 22 December. Due to the short available daylight, only the AlongBay transect was completed. A complete set of up-to-date graphs can be found on the Google Drive: section plots and time sections.
Physical oceanography
Temperature
Recorded water temperatures during this survey ranged from a minimum of 3.7 °C at station AlongBay-13 (1 m depth), in the inner bay off Bear Cove, to a maximum of 5.6 °C at AlongBay-1 (66 m depth) in the outer bay, off Seldovia. There was little indication of vertical stratification, however horizontal differences were evident with warmer waters in the outer bay and coldest waters in the inner bay (Figure 2). A thin surface layer of slightly colder surface water was seen at the head of the bay, an area coinciding with impressive ice fog in the early morning. A local spot of colder water was found off Homer Spit (at about 30 km along-track, Figure 2). Presumably, colder (and fresher) water from Mud Bay, matching the characteristics of waters from the inner-bay, extended out to this area.
On a larger scale, satellite data showed a similar trend for sea surface temperatures, as observed here for Kachemak Bay, for Cook Inlet: warmer waters from the Gulf of Alaska, gradually cooled, as they moved into the increasingly shallow waters of upper Cook Inlet (Figure 3).
Everywhere in the bay, and at all depths, water temperatures were below the long-term mean (top-right of Figure 2). While much of the North Pacific was still in a warm-water anomaly, the Gulf of Alaska had also moved into a negative temperature anomaly, in line with temperatures throughout Kachemak Bay (global SST anomaly). The warm-water anomaly that was a feature in Kachemak Bay waters since the beginning of the year, appeared to have come to an end, at least for now (Figure 4, Figure 5).
Salinity
Salinity values ranged from 29.7 PSU at AlongBay-7 (1m depth) in the outer bay to 31.3 at AlongBay-1 (69m depth) in the outer bay. The outer bay was a little bit more saline than the inner bay. Differences between deep and surface waters were minute, indicating an almost fully mixed water column (Figure 2). Compared to the long-term mean, surface, and especially outer bay waters, were by up to 1 SD saltier.
Similarly to the heat wave years of 2014-16, the bay experienced anomalously warm waters for the first 2/3 of 2025. Since this fall, salinity reverted to being saltier than normal (Figure 8)
Turbidity
The inner bay was more turbid than the outer bay (Figure 2). In contrast to last month, when deep waters were considerably more turbid than surface waters, there was no such contrast this month.
Biological conditions
Phytoplankton
Chlorophyll concentrations were close to zero throughout Kachemak Bay, showing no areas of concentrated activity (Figure 2).
Wildlife
One late humpback whale was feeding off Bear Cove near the head of the bay.
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