The phytoplankton of the Bering and Chukchi seas support highly productive ecosystems characterized by tight benthic-pelagic coupling. In this study, we focus on the northern Bering and Chukchi seas, considering them as one ecosystem. This community has historically been dominated by diatoms; however, climate change and accompanying warming ocean temperatures may alter primary producer communities. Using metabarcoding, we present the first synoptic, high-throughput molecular phylogenetic investigation of phytoplankton diversity in the Bering and Chukchi seas based on hundreds of samples collected from June to September in 2017. We identify the major and minor taxonomic groups of diatoms and picophytoplankton, relative abundances of genera, exact sequence variants (201 for diatoms and 227 for picophytoplankton), and describe their biogeography. These phylogenetic insights and environmental data are used to characterize preferred temperature ranges, offering insight into which specific phytoplankton (Chaetoceros, Pseudo−nitzschia, Micromonas, Phaeocystis) may be most affected as the region warms. Finally, we investigated the likelihood of using shipboard CTD data alone as predictive variables for which members of phytoplankton communities may be present. We found that the suite of environmental data collected from a shipboard CTD is a poor predictor of community composition, explaining only 12.6% of variability within diatom genera and 14.2% variability within picophytoplankton genera. Clustering these communities by similarity of samples did improve predictability (43.6% for diatoms and 32.5% for picophytoplankton). However, our analyses succeeded in identifying temperature as a key driver for certain taxa found commonly throughout the region, offering a key insight into which common phytoplankton community members may be affected first as the Alaskan Arctic continues to warm.

Warm, moderately salty Bering Sea Water (BSW) carried into the Chukchi Sea through Bering Strait provides an oceanic heat flux for melting sea ice comparable to that of the solar heat flux. Intrusions of BSW transport heat and nutrients via intrapycnocline eddies vertically beneath the sea ice and laterally across structural fronts near the ice edge, setting up hydrographic features important to ice edge communities and the seasonal evolution of the ice melt-back. However, the intrapycnocline eddy dynamics and associated hydrography near the fronts have not previously been well described or characterized. Three numerical models using the Regional Ocean Model System (ROMS) are integrated to systematically investigate the importance of the intrapycnocline eddy field and the factors that affect its dynamics. The models suggest that the heat transported by eddies depends on frontal stratification, which is influenced primarily by the Bering Strait inflow discharge and salinity. The eddy field is also indirectly modified by the sea surface height, which varies with strong winds. Two frontal zones near the ice edge are identified according to the model-derived hydrographic structures and eddy dynamics: the Shelf Water Transition Zone (SWTZ) and the Melt Water Transition Zone (MWTZ). Improved understanding of these frontal zones will benefit future research of the ice edge ecosystem. Our models show a noticeable effect of strong wind events on ice edge displacement and vertical transports, both of which may be important to primary production in the frontal zones. Changing winds associated with increasing sea surface temperatures could alter the manifestation of the processes highlighted in this study.

The St. Lawrence Island polynya (SLIP) opens every winter off the coast of St. Lawrence Island as winds move ice away from the shore. The SLIP is an important site for production of the dense water that flows northward through the Bering Strait to help maintain the Arctic Ocean halocline. Winter 1991/1992 ERS-1 SAR, thermal infrared, and passive microwave imagery are analyzed in combination with regional climate system and analytical simulations to investigate SLIP ice circulation, heat fluxes, and dense water production. Emphasis is on the February 1992 southern SLIP event. Satellite-based measurements show this polynya extended ~165km offshore and ~100km along shore at maximum extent. ERS-1 SAR GPS-derived ice motion indicated maximum ice speeds of ~30km day -1 during polynya expansion. Ice along the polynya boundary drifted parallel to the wind at 3--4% of the wind speed during north/northeasterly winds >7m s-1 Heat fluxes associated with the SLIP varied depending on method of calculation, but indicated increasing trends during polynya development. Associated ice production rates of 4.218.9cm day-1 were computed via different models. Dense water production, derived from ice production rates and polynya size, ranged from 0.011--0.017Sv, suggesting that the SLIP could account for 19--27% of the Bering Sea's contribution and 1--2% of the total Arctic contribution to Arctic Ocean halocline maintenance. Although the regional climate system model generated the SLIP on the same time scales as observed, a larger polynya resulted. The simulated polynya's heat and moisture impact was observed to at least 800mb, reaching 50km downstream. During periods of sustained winds, ice circulation was similar to that observed. Incorporation of a "barotropic" ocean component suggested that ocean circulation may be an important ice circulation forcing mechanism at the SLIP, especially during periods of weak winds, as inclusion greatly improved the simulated ice circulation. The "barotropic" ocean also improved polynya shape and extent. If regional climate changes alter the existence of polynyas like the SLIP, changes in the Arctic Ocean halocline might occur. Additional in situ observations and better fully-coupled atmosphere-ice-ocean models are needed to further ascertain the impact of polynyas on the overall Arctic climate system.

This study is a simulation of the circulation of the Greenland Sea aimed at modeling some of the issues related to the Great Salinity Anomaly (GSA) and deep water formation using a primitive equation ocean general circulation model (Semtner, 1974). The features of the model include: (1) a high resolution, (2) real topography, (3) open boundaries at the south and north, and (4) temporally variable wind and thermohaline forcing. The model is used to study: (1) the spreading of a fresh water anomaly, (2) the mechanisms of cross frontal mixing that lead to deep water formation, (3) the general circulation of the deep and upper layers of the ocean and their dependence on wind and thermohaline forcing, and (4) the possible implications of meso-scale and large-scale variability on climate change. One of the major results of this work is the simulation of continental shelf waves propagating along the shelf slope of Greenland between 77$\sp\circ$N and 72$\sp\circ$N. Waves with a subinertial period of 17.2 hrs, a wavelength of 363 km, a phase speed of 586 cm/s and a group velocity of 409 cm/s, are found. Possible mechanism for generation of shelf waves is presented. It is suggested that some energy related with wave activity may support cross-frontal mixing in the East Greenland Current (EGC), where formation of the two main sources of North Atlantic Deep Water (e.g. Norwegian Sea Deep Water and Denmark Strait Overflow Water) have been reported. The results from the GSA simulation suggest that during the early stage of the GSA (e.g. during its propagation with the EGC to the south, in the late 1960s) when no observations are available, the fresh water signal is not being mixed into the interior circulation of the Greenland Sea gyre. The second experiment, representing recirculation of the GSA from the North Atlantic back into the Greenland Sea, in the late 1970s, shows freshening in the Greenland Sea gyre of comparable magnitudes ($-$0.05 to $-$0.1 psu) to the observed ones. These results agree with the earlier indirect measurements (Rhein, 1991; Schlosser et al., 1991) indicating dramatic reduction of deep water renewal in the Greenland Sea in the late 1970s and early 1980s. From the general circulation experiments it has been found that the ocean response to seasonal forcing is mainly barotropic. This implies a strong topographic control in the distribution of currents and hydrographic variables. Most of the areas of topographic steering which are simulated in the region have been reported in the literature. The so-called Molloy Deep eddy shows its direct dependence on the large scale dynamics affecting the northward flow of the West Spitsbergen Current (WSC), controlling this way a net mass transport into the Arctic Ocean. Simulations with different wind forcing suggest dependence of the Greenland Sea gyre circulation on the variations with time of the local wind forcing. Results indicate that monthly mean wind stress forcing probably underestimate wind forcing in the model. Analysis of surface, intermediate and deep ocean velocity fields compare reasonably well with observations.

A series of numerical experiments are performed to simulate the Gulf of Alaska circulation and to examine the dynamical ocean response to the annual mean and seasonal forcing using a primitive equation model (Semtner 1974). The model domain encompasses the North Pacific north of 45$\sp\circ$ N and east of 180$\sp\circ$ and is surrounded by artificial walls in the south and west. Biharmonic diffusion is used in the interior to excite mesoscale eddies. A sponge layer with high Laplacian diffusion is incorporated near the western boundary. Horizontal resolution of 30$\sp\prime$ x 20$\sp\prime$ and 20 vertical levels are used to resolve the mesoscale topography and eddies. Wind stress computed from sea level atmospheric pressure and temperature and salinity data of Levitus (1982) are used. A diagnostic model produces a circulation in the Gulf of Alaska which agrees with observed patterns. In a three-layer flat-bottom baroclinic model, baroclinic Rossby waves propagate at 0.8 cm/sec and it takes a decade for spin-up to be completed. Baroclinic models forced by the annual mean wind and thermohaline forcings show the generation of eddies by baroclinic instability. The eddies in the flat-bottom model have a period of 75 days and are interpreted as barotropic Rossby waves. In the model with topography, the period of dominant eddies is 3-4 years and they are interpreted as baroclinic Rossby waves. Anticyclonic eddies near Sitka show similar characteristics as the Sitka eddy. They propagate westward and cause meanders in the Alaska Stream near Kodiak Island. The abnormal shift of the Alaska gyre in 1981 is probably due to the presence of one of these anticyclonic eddies. A flat-bottom model with seasonal forcing shows a large seasonal variability. When bottom topography is present, however, seasonal response is greatly reduced due to the dissipation of barotropic response by bottom topography. The seasonal baroclinic model shows a similar seasonal variability to the seasonal barotropic model indicating that the seasonal response is mainly barotropic. Eddies are also excited in the seasonal case and are almost identical to those of the annual mean case.

The theme of this dissertation is the importance of effective moisture (precipitation minus evaporation) in subarctic ecosystems. Interior Alaska has a relatively dry climate with annual precipitation ranging from 25--45 cm. Records from interior Alaska lake sediment cores show low lake levels following the Last Glacial Maximum, with significant increases at 12,000 and 9,000 14C years BP. Using lake-level reconstructions and models based on modern hydrologic and meteorologic data, we infer precipitation of 35--75% less than modern at 12,000 yr. BP, 25--45% less than modern at 9,000 yr. BP, and 10--20% less than modern at 6,000 yr. BP. Trees were scarce on the interior Alaskan landscape during the late Pleistocene with birch species appearing about 12,000 BP and spruce species approximately 3500 years later. The correspondence between lake-level and vegetation changes suggests that moisture may have been one of the limiting factors in the establishment of these tree species. Alaska climate records show a climatic regime shift in the mid-1970s. Less effective moisture is available over the past 30 years because summer temperatures in interior Alaska have been increasing without a concurrent increase in precipitation. Radial growth of white spruce at 20 low elevation stands in interior Alaska declined corresponding with this climatic change. The observation that moisture limits spruce growth in Alaska today is consistent with our inference of moisture limitation in the early Holocene. A 200-year reconstruction was developed based on two tree ring proxies, 13C discrimination and maximum latewood density, which together show excellent agreement with the recorded Fairbanks average May through August temperatures. The first half of the 20th century is characterized by the coolest summers of the 200 year period of reconstruction, while the latter part of the 20th century, particularly from 1974 onward, is characterized by some of the warmest summers of the 200 year period. Mid-19 th summer temperatures reconstruct to be as warm as the latter part of the 20th century, which is inconsistent with reconstructions of other regions. It seems likely, based on current information, that these inconsistencies may be real and may reflect regional synoptic conditions unique to interior Alaska. Distinctive decadal scale regimes were identified throughout the record.

Trace metals in the marine environment are found in trace amounts, but are important tracers of oceanographic processes, and bioactive trace metals can impact ocean biogeochemistry through their nutrient or toxic influence of microbial populations. Sea ice is an intrinsic feature of the Arctic Ocean that likely plays a key role in the cycling of trace metals, given that this substrate can concentrate, alter, and transport these elements. Warming conditions in the Arctic have decreased sea ice cover over the past decades and the loss of sea ice threatens to drastically change the Arctic ecosystem, but the implications are not entirely understood. The scarcity of studies on Arctic sea ice entrained trace metals is due in part to the lack of commercially available sampling equipment capable of collecting sea ice without introducing contamination, and in part to the logistic and economic difficulties in accessing remote Arctic sea ice sites. Natural heterogeneity related to large sediment loads incorporated in uneven patches across Arctic fast ice poses a challenge when designing observational studies of trace metals in sea ice. The scope of this thesis is on the study of trace metals in Alaskan Beaufort Sea fast ice environment. The study includes snow, sea ice and seawater under the ice. Analysis of dissolved (Mn, Fe, Cu and Zn) and particulate (Al, Mn, Fe, Cu and Zn) phases was carried out from 50 ice cores collected with a trace metal clean ice corer developed at the University of Alaska Fairbanks. The results of this study indicated that the ice corer developed at UAF was able to collect uncontaminated samples. Highly variable and elevated concentrations of particulate (> 0.2 μm) trace elements were observed due to the notable variability in the amount of sediment incorporated within ice cores, but surprisingly dissolved (< 0.2 μm) metal concentrations were relatively low and consistent. The observed low dissolved metal concentrations, along with low bulk salinity and low percent leachable particulate trace metal fractions, suggest that desalination removed reactive metals from the ice matrix prior to sampling. Spatial variability of dissolved and particulate trace metals was statistically analyzed and indicated generally negligible variability on the meter scale, but significant variability on the kilometer scale, for both size classes. These results emphasize that future studies of trace metals in sea ice should include temporal and spatial considerations.

Prince William Sound is a complex fjord-type estuarine system bordering the northern Gulf of Alaska. This study is an analysis of exchange between Prince William Sound and the Gulf of Alaska. Warm, high salinity deep water appears outside the Sound during summer and early autumn. Exchange between this ocean water and fjord water is a combination of deep and intermediate advective intrusions plus deep diffusive mixing. Intermediate exchange appears to be an annual phenomenon occurring throughout the summer. During this season, medium scale parcels of ocean water centered on temperature and NO maxima appear in the intermediate depth fjord water. Deep advective exchange also occurs as a regular annual event through the late summer and early autumn. Deep diffusive exchange probably occurs throughout the year, being more evident during the winter in the absence of advective intrusions.

Time series of monthly means up to 65 years long were examined to determine the time and spatial scales of variablity in the Gulf of Alaska. Sea level, sea level pressure (SLP), air temperature, fresh water discharge, sea surface temperature (SST) and the Southern Oscillation Index (SOI) are the variables chosen to gain insight into local and global responses in the gulf. This study reports four major results. 1) Sea level anomalies (variations from the annual cycle) are driven by wind and fresh water; temperature effects in sea level are not seen. 2) SST anomalies cannot be predicted from sea level data, but SLP in southeastern Alaska and air temperature in Seward may be useful indicators on a two to three month time scale. 3) On the whole, anomalies in coastal and interior Alaska weather occur together, with SLP 180° out of phase with air temperature and precipitation. Using empirical orthogonal functions, the Southeast and Southcoast district can be separated. 4) A statistically significant SOI signal is seen is both SLP (p>0.995, Seward) and sea level (p>0.995) records.