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Marine Ice Atlas for Cook Inlet, Alaska
Abstract
Cook Inlet, a 350-km-long estuary located in south-central Alaska,is a region of great importance to the economy of the entire state. Approximately half the population of Alaska resides near its shores, and Anchorage, at its northern end, is the state's largest city and a focus for commerce, industry, recreation, and transportation. Tidal height variations at Anchorage are the second most extreme in the world, exceeded only by those in Canada's Bay of Fundy. Cook Inlet's extreme tidal range and the shallow bathymetry produce extreme tidal currents as well. During winter the marine ice that forms in the Inlet can have a substantial impact on human activities. This report is a compilation of previously published and unpublished information on the climatic, meteorological, oceanographic,and hyrodynamic conditions that influence the marine ice cover in Cook Inlet. Biweekly maps, based on historical conditions from 1984 through 1999, are presented that show the expected concentrations and stages of development of the ice cover.These maps were produced by re-analyzing approximately 675 archived ice charts that were produced by the National Weather Service between 1984 and 1999, using ArcView TM GIS software.
... To provide a meaningful summary of tracking and diving metrics, we analyzed the data set as a whole to assess overall beluga behavior, and separately, as two seasonal periods, to assess beluga behavior in the presence and absence of ice. The two seasonal periods were based on the average significant appearance and disappearance of ice in northern Cook Inlet over a 17-year period (November 25 (SD ± 17 days) and April 9 (SD ± 18 days) between 1969 and 1985) (Mulherin et al. 2001). Using December as the cut-off between ice-covered and ice-free months in Cook Inlet, we divided the data into two equal time intervals: June-November and December-May. ...
... December (Mulherin et al. 2001). Ice extent and thickness peaks in mid-February and breaks up between March and May. ...
... Ice extent and thickness peaks in mid-February and breaks up between March and May. During colder winters, ice may extend into the lower Inlet approaching the Gulf of Alaska (Mulherin et al. 2001). The large amounts of freshwater entering Knik Arm and Turnagain Arm contribute to relatively high concentrations of ice in these areas over the winter. ...
... Studies of these populations, combined with the results reported here, indicate that some beluga populations can be considered " year-round residents " and do not make the annual long-distance migrations between summering and wintering grounds observed for other beluga populations (Richard et al., 1998Richard et al., , 2001a, b; Martin and Smith, 1999; Suydam et al., 2001). Tidal fluctuations in Cook Inlet (9 m) are among the most extreme in the world (second only to those in Canada's Bay of Fundy), and the tidal range produces extreme tidal currents ranging from 2 – 4 m/second (Mulherin et al., 2001). Tides have been documented to influence beluga movements in other areas (Kleinenberg et al., 1964; Caron and Smith, 1990 ). Belugas in Cook Inlet have been observed moving into the upper reaches of the inlet during flood tide and departing during ebb tide (Moore et al., 2000; ). ...
... Ice cover in Cook Inlet is seasonal, forming in the fall (generally October) and disappearing completely in the spring. By December, about half the inlet north of the Forelands is normally covered in pancake ice (up to 10 cm thick) and thin ice (30 – 70 cm thick) ranging in concentration primarily from open (10%) to close pack (70% to 80%) (Mulherin et al., 2001). The ice extent and thickness increase through late January and February, reaching maximums in mid-February to early March. ...
... The ice extent and thickness increase through late January and February, reaching maximums in mid-February to early March. During colder winters, the ice may extend into the lower inlet south of Chinitna Bay on the west side and to approximately 60˚N60˚N (north of Homer) on the east side (Mulherin et al., 2001). It has been well documented that belugas can tolerate extreme concentrations of sea ice. ...
Seasonal movements of 14 belugas in Cook Inlet, Alaska, were monitored by satellite telemetry between July and March in 2000-03. Whales used waters in the upper Cook Inlet intensively between summer and late autumn and dispersed to mid-inlet offshore waters during winter months. All whales remained in Cook Inlet the entire time they were tracked, and several whales were tracked through March. During summer and early fall, movements were clearly concentrated in specific areas, generally river mouths or bays, where whales were likely feeding on fish runs. Average daily travel distances ranged from 11 to 30 km per day. Monthly home ranges, estimated using the 95% kernel probability distribution of average daily positions, were smallest in August (982 km2), increased throughout autumn, and peaked in winter (reaching approximately 5000 km 2). The seasonal variation in distribution and movement patterns displayed by belugas in Cook Inlet affect the sighting rates and seasonal abundance estimates obtained for this depleted population.
... The Cook Inlet is a semi-enclosed, subarctic tidal estuary on the southern coast of Alaska composed of three main regions: the Head, the Upper and the Lower Inlet [5,6], (Fig.1). It is approximately 330 km long, 48 km wide and no more than 60 m depth. ...
Marine renewable energy deployment involves site resource assessment as strategic support for installation and optimization. This part of the design needs to be based on best available measurement technologies and deployment methods, minimizing the investments. The siting and design of a kinetic energy converter (like a Tidal Energy Converter ones) require characterization of the variability of the flow velocity acting on the energy capture area in space and time, in order to assess the hydrodynamic forces, to design the structural loading and power capacity of the TEC, helping investment decisions and project financing. In this work, a site assessment procedures for emplacement of TEC machines are shown, comparing sites with different hydrogeological characteristics using the same design approach. In order to define the best conditions for siting, three case studies have been carried out, two for sea and last for river installation. The strait of Messina (Italy), a marine channel with an amphidromic point for the tides, has its minimum depth at 72 m, between Ganzirri and Punta Pezzo, deepening to 1000 m to the North East and down to 2000 m to the South. The Cook Inlet (Alaska), a large subarctic estuary in South-central Alaska which extends about 250 km from Anchorage bay to the Pacific Ocean. Tidally dominated currents control the hydrographic regime, meanwhile water levels and currents are influenced by tides coming from the Gulf of Alaska, which are significantly amplified as approaching Anchorage bay. The Pearl River Estuary and its adjacent coastal waters (China) have a length of about 70 km, a width of about 15 km and an average depth of about 4.8 m, but it has a depth of more than 20 m in its eastern part.
... The Cook Inlet is a semi-enclosed, subarctic tidal estuary on the southern coast of Alaska [5] (Fig.1). It is approximately 330 km long, 48 km wide and no more than 60 m depth. ...
The siting and design of a Tidal Energy Converter (TEC) require the characterization of the flow velocity field acting in terms of space and time, in order to assess the hydrodynamic forces, to calculate the structural loading and power capacity, also helping investment strategy and project financing. In this framework, the selection of the emplacement site is of paramount importance for optimizing efficiency of TEC. In this study, we propose site assessment procedures for emplacement of TEC machines, comparing a sea tidal site with two rivers ones. Sites differ each other from geomorphological characteristics. The Cook Inlet (South-Central Alaska) is a large subarctic estuary, which extends about 250 km from Anchorage bay to the Pacific Ocean. Tidally dominated currents control the hydrographic regime, with water levels and currents periodically influenced by tides from the Gulf of Alaska, which are significantly amplified as approaching Anchorage bay. The Cháng Jiāng river (also named Yangtze, China) is the longest in Asia and the third in the world, with a huge flow rate. The Pearl River Estuary (China) has a length of about 70 km, a width of about 15 km and an average depth of about 4.8 m. It is deeper than 20 m in its eastern part, and discharges into a microtidal environment along the northern shelf of the South China Sea. The TEC performances have been compared in the three different geomorphological environments. Results show how TEC in rivers can perform up to 5.47 kW/m², a huge value compared to the wide sea turbines, able to perform up to 10.76 kW/m².
... Sea ice is found over Cook Inlet for 6-8 months of the year (October-November to March-April, Mulherin et al. 2001) and could have an effect on the ambient and waterborne industrial sounds. The ice might increase the noise from turbulence due to tidal flow, increasing the low-frequency ambient levels. ...
... Sea ice is found over Cook Inlet for 6-8 months of the year (October-November to March-April, Mulherin et al. 2001) and could have an effect on the ambient and waterborne industrial sounds. The ice might increase the noise from turbulence due to tidal flow, increasing the low-frequency ambient levels. ...
The Matanuska–Susitna Borough is the fastest growing region in the State of Alaska and is impacted by a number of human activities. We conducted a multiscale assessment of the stressors facing the borough by developing and mapping the Index of Watershed Integrity (IWI) and Index of Catchment Integrity (the latter considers stressors in areas surrounding individual stream segments exclusive of upstream areas). The assessment coincided with the borough’s stormwater management planning. We adapted the list of anthropogenic stressors used in the original conterminous United States IWI application to reflect the borough’s geography, human activity, and data availability. This analysis also represents an early application of the NHDPlus High Resolution geospatial framework and the first use of the framework in an IWI study. We also explored how remediation of one important stressor, culverts, could impact watershed integrity at the catchment and watershed scales. Overall, we found that the integrity scores for the Matanuska–Susitna basin were high compared to the conterminous United States. Low integrity scores did occur in the rapidly developing Wasilla–Palmer core area. We also found that culvert remediation had a larger proportional impact in catchments with fewer stressors.
Measurements of oxygen and hydrogen stable isotopes in precipitation (δ18OP and δ2HP) provide a valuable tool for understanding modern hydrological processes, and the empirical foundation for interpreting paleoisotope archives. However, long-term datasets of modern δ18OP and δ2HP in southern Alaska are entirely absent, thus limiting our insight and application of regionally defined climate-isotope relationships in this proxy-rich region. We present and utilize the first long-term record (13 years) of event-based δ18OP and δ2HP data from Anchorage, Alaska (2005-2018, n=332) to determine the mechanisms controlling precipitation isotopes. Local surface air temperature explains ~30 % of variability in the δ18OP data with a temperature-δ18O slope of 0.31 ‰/°C, indicating that δ18OP archives may not be suitable paleo-thermometers in this region. Instead, back-trajectory modelling reveals how winter δ18OP/ δ2HP reflects synoptic and mesoscale processes in atmospheric circulation that drive changes in the passage of air masses with different moisture sources, transport, and rainout histories. Specifically, meridional systems –with either northerly flow from the Arctic or southerly flow from the Gulf of Alaska – have relatively low δ18OP/δ2HP due to progressive cooling and removal of precipitation as it condenses with altitude over Alaska’s southern mountain ranges. To the contrary, zonally derived moisture from either the North Pacific and/or Bering Sea retains relatively high δ18OP/δ2HP values. These new data contribute a better understanding of the modern Alaska water isotope cycle and provide an empirical basis for interpreting paleoisotope archives in context of regional atmospheric circulation.
Cook Inlet beluga whales (CIBs) are an endangered population residing in Cook Inlet, Alaska. We characterized the calling behavior of CIBs to improve our understanding of sounds produced by this population. Bottom-moored hydrophones were deployed at Eagle Bay in summer 2009 and at Trading Bay in summer and winter 2009. CIB sounds were qualitatively analyzed and categorized as a whistle, pulsed call, or click train. A total of 4,097 calls were analyzed, and 66 unique whistle contours were identified. Whistles were quantitatively analyzed using a custom Matlab program. A chi-square test showed the call category usage at Eagle Bay during summer 2009 and those at Trading Bay during summer 2009 and winter 2009–2010 differed significantly (P < 0.001). Pulsed calls were more common during summer months, and click trains within the frequency band (12.5 kHz) were more common in Eagle Bay. The variation in calling behavior suggests differences in habitat usage or in the surrounding environment, including background noise. With the proposed development projects in Cook Inlet and the potential increase in ambient noise level due to ocean acidification, it is important to understand how this endangered population uses sound, and what anthropogenic factors may influence that use.
The annual abundance population estimates of the endangered beluga
whales in Cook Inlet (CI), Alaska, have indicated a decline in the
population over the past decades and no convincing explanation has been
offered so far for this trend. Satellite tracking data of about 20 Cook
Inlet beluga whales (CIBW) over some 5-year period, as well as annual
population counts and stranding reports were compared with environmental
observations. The seasonal movements of the belugas within CI appear to
be affected by variations in water temperature, ice coverage and most
significantly, by river discharge. Statistically significant
correlations were found between the seasonal movements of the CIBW and
the timing of peak flows at different rivers. Interannual variations of
the CIBW movements were found to relate to year-to-year variations in
water temperature and the time of ice melt/freezing; thus, in warmer
years the CIBW will stay in the upper inlet longer, before dispersing to
the mid and lower CI in winter. Both, the population of the beluga and
stranding numbers show a 3-4-year cycle of interannual variations
resembling the Pacific Decadal Oscillation (PDO) index, though the exact
mechanism in which large-scale climate variations impact the CIBW
habitat is not clear yet. The analysis suggests that the method of
estimating the CIBW population from annual aerial surveys needs further
evaluation, since interannual changes in the spatial distribution of
CIBW preferred locations may have a confounding effect on estimates of
population abundance.
Surface waters in the Gulf of Alaska undergo a net dilution throughout most of the. year since the regional precipitation exceeds evaporation. Recent hydrographic data give evidence that seasonal dynamic height fluctuations in the upper layers ( 130 cm year−1), runoff, longshore accumulation of fresh water around the gyre, and the low water temperatures. The coastal sea level is in phase and has nearly the same amplitude as the local dynamic height, though not in phase wit...
Because of shortcomings in the current wind chill formulation, which did not consider the metabolic heat generation of the human body, a new formula is proposed for operational implementation. This formula, referred to as the Steadman wind chill, is based on peer-reviewed research including a heat generation and exchange model of an appropriately dressed person for a range of low temperatures and wind speeds. The Steadman wind chill produces more realistic wind chill equivalents than the current NWS formulation. It is easy to determine from tables (calculated by application of a quadratic fit in both U.S. and metric units) with values accurate to within 1°C.
About 20 years ago a number of unique offshore platforms were installed in Cook Inlet, AK. To date, these structures are still the only oil and gasplatforms operating in an ice environment. Although originally designed for a20-year field life, higher oil prices and the discovery of field extensionsmake it likely that several of these platforms will remain in place for as longas 50 years. This paper reviews the design and installation methods developedfor these platforms and describes the inspection procedures and thecorrosionprevention measures that have prolonged the lives of these structures.prolonged the lives of these structures.
Introduction
During the early 1960's four oil fields and one gas field were developed in Cook Inlet, AK. These fields (Figs. 1 and 2) were placed on production with 14self-contained placed on production with 14 self-contained drilling andproduction platforms (Table 1), which were installed during 1964-68. Anotherplatform was installed in 1986. The rapid development of these five fields wasan extraordinary accomplishment because environmental conditions in Cook Inletmake it one of the most difficult offshore areas in which to operate. Thecombination of ice, tides, current, bitter cold, and earthquakes made thedesign, fabrication, and installation of these platforms a formidable technicalchallenge. This rapid development was possible 20 years ago because an aura ofcooperation existed among the oil industry, the responsible governmentalagencies, and the public. It is questionable whether the same type ofdevelopment could be accomplished today in two or three times the length oftime, if at all. The discovery of the immense Prudhoe Bay field on Alaska's North Slope shortly after production from Cook Inlet began has overshadowedthese accomplishments and made this remote corner of the world an almostforgotten offshore area. Yet, even today, the Cook Inlet platforms are the onlyfixed offshore drilling and production platforms anywhere in the world thatoperate platforms anywhere in the world that operate in an ice environment. Theinitial development plans for Cook Inlet fields anticipated an economic fieldlife of about 20 years, and the platform designs were based on this assumption. These 20 years, however, have passed and, because of new field extensions andsecondary recovery projects, it now appears that several of the fields have afurther remaining economic life of 25 years or more. This implies that theplatform structures must also remain in place for this period of time becausereplacing place for this period of time because replacing them, at least atcurrent oil prices, is not economical. That this platform life extension ispossible is attributable to the conservative design-criteria assumptions thatwere used and to an early recognition that special measures were needed toarrest the high corrosion rate of the underwater portions of the platformstructures. This paper provides a retrospective of the design and installationmethods developed for these unique platforms and describes the inspectionprocedures and corrosion prevention measures that have been taken to preventionmeasures that have been taken to prolong the lives of these structures. prolongthe lives of these structures. Environmental Conditions
Cook Inlet is located in southern Alaska (Fig. 1) and penetrates 170 miles[270 km] inland from the Gulf of Alaska. Table 2 summarizes the area'senvironmental conditions. Because of the shape of Cook Inlet and its northernlatitude, tides are among the highest in the world, ranging up to 30 ft [9 m]. The resulting high currents keep the water turbulent most of the time, and somuch sand and glacial flour is in suspension that underwater visibility is nil. Upper Cook Inlet, the area of oil activity, is covered with ice during thewinter months. Ice can be expected as early as November and as late as May. Theinlet is ice-free the remainder of the year. During periods of ice cover, thetides move the ice periods of ice cover, the tides move the ice up and down theinlet at essentially the same speed as the water current. Bottom and subsurfacesoil conditions vary greatly, ranging from soft unconsolidated clays on thewest side of the inlet to boulder-covered, extremely stiff clays on the middleand the east side. Cook Inlet is in the Pacific earthquake belt and, asevidenced by the widespread damage from the 1964 Good Friday earthquake, structures in the inlet are subject to potentially large earthquake loadings.potentially large earthquake loadings. Environmental Forces
Winter sea ice is the principal environmental force imposed on Cook Inletstructures. In 1963, when the first oil field was discovered, very littleinformation was available on the characteristics and strength of the sea icegenerated during the winter months in Cook Inlet.
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Infrared data gathered by the NOAA 3 and 4 satellites have made it possible to construct a detailed synoptic view of sea surface temperatures in the northern Gulf of Alaska. These satellite data are compared with simultaneous oceanographic data to yield information on vertical subsurface features.
Generally two surface temperature regimes characterize the northern gulf throughout the year. Relatively Warm surface water occurs over the continental shelf, while colder water is found farther offshore, beyond the shelf break. A narrow (5–10 km) coastal band, with relatively low temperatures, apparently due to terrestrial runoff, was not always present. Wave or eddy-like features were observed along the boundary between the warm and cold surface water regimes.
Lateral advection and vertical mixing both contribute to maintenance of these two major surface temperature regimes. Offshelf lateral advection and/or upwelling brought colder water into the northern gulf between July 1974 and February 1975, and led to an offshelf temperature decrease of nearly 2°C at 200 m depth. Such temperature decreases at depth were not evident in the shelf waters. The upper layer (<100 m) vertical stability was greater in the offshelf region, and confined the sea-air heat loss there to a relatively shallow layer. Since the water density is controlled primarily by salinity at the temperatures and salinities found in the Gulf of Alaska, sea surface temperature changes reflect both heat loss and vertical density (salinity) structure.
Recent data from the northwest Gulf of Alaska reveal a coastal current which flows westward along the Kenai Peninsula (mainly within 30 km of shore), enters Shelifof Strait, and exits to the southwest of Kodiak Island. This flow, which we call the Kenai Current, has a large seasonal variation in baroclinic transport and maximum surface speed; transport is typically about 0.3×106 m3/s but exceeds 1.0×106 m3/s in fall, with concurrent speed increases from 15-30 cm/s to over 100 cm/s. The coastal flow is clearly distinct from the offshore Alaskan Stream; its seasonal signal is mainly related to a cross-shelf pressure gradient, which responds to an annual hydrological cycle. Current records from Shelikof Srait substantiante the presence of an annual signal and indicate that wind forcing has maximum effect from December through February, but it does not appear to augment flow at other times.
Analyses of wind, adjusted sea level, temperature, salinity, and current
data show that the Alaska Coastal Current (ACC) flows generally westward
from Shelikof Strait to the Shumagin Islands. The seasonal nature of the
ACC in the western Gulf of Alaska is similar to that in the northern
gulf, but minimum salinity, maximum current speeds, and changes in
baroclinic transport are less extreme to the west. Southwest of Shelikof
Strait the ACC apparently is bifurcated by the bathymetry. One branch
continues flowing along the Alaska Peninsula, and the other flows south.
The southward flowing branch may rejoin the westward flowing one in the
sea valley just east of the Shumagin Islands.
Analysis of the time series of the temperature and salinity in the northern Gulf of Alaska from December 1970 to September 1983 shows annual signals in water properties with warm, low-salinity surface water in summer and cold, high-salinity surface water in late winter. The mean surface temperature and salintiy were 11.5°C and 27.33% in summer and 4.3°C and 31.16% in winter. Over the nearly 13-year observational period of surface temperature range was from 2° to 14°C and the surface salinity range was 26 to 31.5%. Abnormal warming throughout the water column was evident in 1976-1977 and 1983. These thermal features appear to be caused by advection, rather than local effects. The salinity anomalies in the upper 50 m are primarily correlated with freshwater discharge and secondarily with wind stress.