UNITED STATES

DEPARTMENT OF COMMERCE

Gary Locke

Secretary

NATIONAL OCEANIC AND

ATMOSPHERIC ADMINISTRATION

Jane Lubchenco

Under Secretary for Oceans

and Atmosphere/Administrator

Office of Oceanic and 

Atmospheric Research

Richard W. Spinrad

Assistant Administrator

NOAA Technical Memorandum OAR PMEL-145

RETROSPECTIVE ANALYSIS OF SEA SURFACE TEMPERATURE IN

THE NORTHERN BERING AND CHUKCHI SEAS

Carol Ladd

James E. Overland 

NOAA/Pacific Marine Environmental Laboratory

Seattle, WA

Pacific Marine Environmental Laboratory

Seattle, WA

June 2009
NOTICE from NOAA

Mention of a commercial company or product does not constitute an endorsement by

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opinions, findings, and conclusions or recommendations expressed in this material are those

of the authors and do not necessarily reflect the views of the National Oceanic and Atmospheric Administration.

Contribution No. 3263 from NOAA/Pacific Marine Environmental Laboratory

Also available from the National Technical Information Service (NTIS)

(http://www.ntis.gov)

ii
Contents iii

Contents

Abstract 1

1 Introduction 1

2 Data 2

2.1 Atmospheric . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2

2.2 Oceanic . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2

3 Atmospheric Surface Air Temperature Time Series 3

4 Spatial Patterns of SST (10-m average temperature) 5

5 Spatial and Temporal Variability in SST 6

5.1 July . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7

5.2 August . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7

5.3 September . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11

6 Temporal Variability in Bering Strait 11

7 Discussion and Summary 13

8 Acknowledgments 15

9 References 16

Retrospective analysis of sea surface temperature in the northern

Bering and Chukchi seas

C. Ladd and J.E. Overland

Abstract. Sea surface temperature (SST) data from the Chukchi and northern Bering seas

beginning in the 1920s are analyzed to investigate low-frequency variability. Although surface air

temperatures at Nome, AK, and adjacent weather stations show a shift in the late 1930s and a

strong warming signal after 1977, spatial variability and sparse oceanic sampling make it impossible

to draw robust conclusions regarding low-frequency temporal variability in SST. Given the data at

hand, however, there is no conclusive evidence for decadal-scale or regime-shift variability in SST in

the northern Bering/Chukchi Sea region during the 20th century, and the data can be considered to

be a single climatology. The warmest SSTs ever measured in eastern Bering Strait were obtained in

2004 during a RUSALCA cruise, and the warmest temperatures measured in western Bering Strait

were observed in 2006, providing evidence that we are seeing a distinct warm period in the current

decade relative to the 20th century. A cruise from 1880 shows SSTs consistent with the 20th-century

climatology.

1. Introduction

Major changes in the Arctic environment have occurred over recent decades.

These changes include changes in sea ice extent (e.g., Nghiem et al., 2007;

Stroeve et al., 2008), oceanography (Polyakov et al., 2007; 2003) and ecosystems (Grebmeier et al., 2006). It is important to document 20th-century

baseline conditions in the Pacific Arctic so that we can understand how

things are changing. This study evaluates available sea surface temperature

(SST) records in the Northern Bering Sea and the Chukchi Sea to assess how

conditions have changed within the last decade and to provide a baseline for

the future.

Many studies have focused on variability in the Arctic over larger spatial

scales (e.g., Polyakov et al., 2007; Steele et al., 2008). Changing sea ice extent has been the most dramatic example of the effects of global warming on

the Arctic and many studies have evaluated the causes of sea ice variability

(e.g., Maslanik et al., 2007; Nghiem et al., 2007). Steele et al. (2008) evaluate

trends in SST in various regions of the Arctic. They find no strong trends

in the Bering and Chukchi Seas before the late 1990s. Steele et al. (2008)

averaged over relatively large regions over which differing processes are regionally important. We examined changes in SST over the northern Bering

Sea and the Chukchi shelves especially surrounding the North Pacific 1976

regime shift. Unfortunately, there are major data gaps in the 20th century

SST records; but our purpose is to summarize what is available.

Spatial patterns of summertime SST are addressed using all available

ocean temperature data. An emphasis on temporal variability at smaller

spatial scales in Bering Strait is possible due to the higher density of data

collected over the years. The flow through Bering Strait is the only connection between the Pacific and the Arctic. This flow has been shown to influence ice melt (Paquette and Bourke, 1981) and stratification (Shimada et al.,

2001; Steele et al., 2004; Woodgate et al., 2005a) in the Arctic. Much recent
2 Ladd and Overland

work with year-round moorings has been accomplished in Bering Strait (i.e.,

Roach et al., 1995; Woodgate et al., 2005b; 2006). Our aim is to put these

recent measurements into a historical context.

2. Data

2.1 Atmospheric

To evaluate the large-scale atmospheric temperatures, monthly mean surface

air temperature data from Nome and Kotzebue, AK, and Providenja and

Mys Uelen, Russia, were downloaded from the National Climatic Data Center (http://www.ncdc.noaa.gov/oa/ncdc.html). These four temperature

records are significantly correlated with each other. Because the Nome temperature record is the longest (1907–2006), we use those data. A monthly

climatology for Nome surface air temperature was constructed by averaging

all data from each month.

2.2 Oceanic

Ocean temperature data from the World Ocean Database (WOD05) (Johnson et al., 2006) were downloaded from the Ocean and Weather Data Navigator (http://dapper.pmel.noaa.gov/dchart/) for the region 175◦E–160◦W,

62◦–72◦N. After removing profiles positioned over land, as well as outliers

and empty stations, the total dataset consisted of 18,698 profiles. The majority of these profiles (14,831) were collected during the summer months

(July, August, September), so we restrict our analysis to those 3 months.

After removing those profiles that had no data in the top 10 m, the resulting

dataset consisted of 14,384 profiles spread relatively evenly between the 3

months (Fig. 1). While the earliest profiles in the dataset were collected in

1855, the dataset includes only 32 profiles prior to 1925. Because many of

the profiles do not have data right at the surface, SST is defined here as the

mean temperature over the upper 10 m. The scattered profile data were gridded to a regular grid using objective mapping as in Kessler and McCreary

(1993) with mapping scales of 0.5◦ in both latitude and longitude.

Additional temperature data not included in WOD05 were obtained from

the Russian-American Long-term Census of the Arctic (RUSALCA) program

for August 2004, 2005, and 2006, and September 2007. In particular, we

discuss transects across Bering Strait. In addition, a transect across Bering

Strait taken on 5 September 1880 (but not included in WOD05) is discussed

(Dall, 1882).
Sea surface temperature in northern Bering and Chukchi seas 3

3. Atmospheric Surface Air Temperature

Time Series

Climatological surface air temperatures ranged from –15.0◦C in January to

10.4◦C in July. Not surprisingly, variability was greatest in winter months

(January standard deviation = 4.8◦C) and lowest in the summer months

0

1000

2000

3000

4000

5000

6000

No. Stations

Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec

1900 1950 2000

Year

0

200

400

600

800

1000

No. Stations

4463

6047

3874

Figure 1: Histogram showing temporal distribution of ocean temperature profiles.
4 Ladd and Overland

J FMAMJ J A S ON D

Number of Standard Deviations

Figure 2: Nome surface air temperature anomalies normalized by monthly standard deviation. Anomalies calculated with respect to monthly climatology.

(July standard deviation = 1.4◦C). After removing the climatology and normalizing by the monthly standard deviation, Nome temperatures exhibit

anomalously high temperatures from 1977 to present (Fig. 2). This “regime

shift” has been widely studied and has been attributed to a deepening Aleutian Low (Overland et al., 1999) and reduced SLP in the Arctic (Savelieva

et al., 2000).

A short period from the late 1930s to the early 1940s also exhibits anomalously high air temperatures. A composite time series of Arctic surface air

temperatures covering the entire Arctic showed that high-latitude temperature was higher in the late 1920s through the early 1940s than in recent
Sea surface temperature in northern Bering and Chukchi seas 5

decades (Polyakov et al., 2003). However, when only the region surrounding

the Northern Bering and Chukchi seas (Nome, Kotzebue, Providenja, and

Mys Uelen) is analyzed, this earlier warm period is not as strong or as persistent as the recent (post-1977) warm period. At Nome, anomalously warm

temperatures in the 1930s–1940s occurred primarily in the spring and fall

(April and October), while summer anomalies were <1 standard deviation

from the mean (Fig. 2); this event is considered to relate to El Ni ̃no conditions. The post-1977 event extends over decades, showing warm anomalies

greater than one standard deviation throughout the year.

4. Spatial Patterns of SST (10-m average

temperature)

Objective maps of all data in each summer month illustrate the spatial patterns of SST (Fig. 3). Here we plot only July data, but patterns are similar

in August and September. Norton Sound exhibits the warmest temperatures

in our study region. SST in Norton Sound (165–161◦W, 63–64.5◦N) average

9.0◦C, 12.0◦C and 8.6◦C in July, August, and September, respectively. The

warm SSTs in Norton Sound are likely due to the shallow depths and the

riverine input that stratifies surface waters.

Surface temperatures in Bering Strait reflect the three water masses that

flow through the strait (Coachman et al., 1975). Alaskan Coastal Water

is relatively warm and flows through the eastern channel of Bering Strait

continuing northeastward along the Alaskan coast. Anadyr Water, colder

than Alaskan Coastal Water, flows from the Gulf of Anadyr, through Anadyr

Strait west of St. Lawrence Island, and through the western channel of

Bering Strait. Bering Shelf Water in the middle of the strait is generally

formed as a mixture of Anadyr Water and Alaskan Coastal Water.

These patterns (warmer in the east, colder in the west) continue into the

southern Chukchi Sea, reflecting the continuation of the Alaskan Coastal

Current along the coast of Alaska (Coachman et al., 1975). The coastal

current bifurcates near Point Hope with transport to the northwest along

the Hope sea valley in addition to northward transport to the east of Herald

Shoal (Ahln ̈as and Garrison, 1984; Coachman et al., 1975; Overland and

Roach, 1987). This bifurcation is reflected in a tongue of warmer water

extending offshore from the Alaskan coast near Point Hope (Fig. 3). These

flow patterns have been shown to influence the melt-back patterns of sea ice

(Paquette and Bourke, 1981). The colder water over Herald Shoal results

from a Taylor column that traps ice and cold water above the shoal and

results in later ice melt than in the surrounding water (Martin and Drucker,

1997).

Cold temperatures along the northern Siberian coast are associated with

the Siberian Coastal Current (Weingartner et al., 1999). This region is

influenced by winds, Siberian river outflows, and ice melt. The Siberian

Coastal Current usually converges with the northward flow through Bering
6 Ladd and Overland Degrees C

Siberia

Alaska

Bering

Strait

Norton

Sound

Kotzebue

Sound

Point

Hope

Hope Sea Valley

Herald

Shoal

Wrangel

Island

Long

Strait

Gulf of

Anadyr

Anadyr

Strait

St Lawrence

Island

Anadyr

Strait

Figure 3: Objective map of SST (◦C) using all available July data. Bathymetry (m) is overlaid (light blue

contours).

Strait and is deflected offshore. Some indication of the offshore deflection in

the cold SSTs offshore of the 50-m isobath near ∼70◦N is evident (Fig. 3).

The Siberian Coastal Current occasionally flows southward through Bering

Strait, especially in fall and early winter when northerly winds are strong

(Weingartner et al., 1999).

5. Spatial and Temporal Variability in

SST

Unfortunately, insufficient SST data exist to determine whether significant

shifts in regional oceanographic conditions occurred at the same time as the

shifts in Nome surface air temperatures. To characterize the changes in SST

patterns surrounding the 1977 regime shift, we divide the dataset into preand post-1977 periods (1977 is included in the latter period). We use all

WOD05 data to form composites of the two periods and look for differences.

These differences are not statistically significant but do provide suggestions
Sea surface temperature in northern Bering and Chukchi seas 7

of where, and by how much, conditions may have changed. Coherent spatial

patterns lend confidence to these results.

5.1 July

In July, north of Bering Strait, SSTs on the eastern side of the basin were

warmer after 1977 by up to 4◦C (Fig. 4). Warmer temperatures were

also apparent crossing the Chukchi Sea in a northwesterly direction from

Point Hope, reflecting the previously mentioned bifurcation of the Alaskan

Coastal Current. The July post-1977 SST map was heavily dominated by

data from 1986–1989, while the pre-1977 data were more distributed over

many decades. During the mid-1980s, the Yukon River discharge at Eagle, AK, was above average for June and July (http://nwis.waterdata.

usgs.gov/ak/nwis/nwisman/?site_no=15356000&agency_cd=USGS). The

resulting increased stratification of the Alaskan Coastal Current may have

contributed to the warmer temperatures during that time period.

Unfortunately, after 1976, no July data exist south of Wrangel Island

(along the north Siberian Coast west of ∼178◦W). However, the data east

of 178◦W on the north Siberian Coast and through the west side of Bering

Strait indicate cooler SSTs (by 2–3◦C) after 1977. Again, the post-1977

map is heavily dominated by 1986–1989 data. The cooler waters on the

western side of Bering Strait could be due to an enhanced Siberian Coastal

Current with increased southward intrusions through Bering Strait. This

conjecture is supported by evidence that annual mean transport through

Bering Strait in 1987 and 1988 was much lower than average (Roach et al.,

1995). The cooler temperatures in the western side of Bering Strait could

also be due to changes in the properties of the Anadyr Water that flows

northward through Anadyr Strait and into Bering Strait. There is some

indication of colder SSTs in the Gulf of Anadyr (Fig. 4).

5.2 August

The warming of the Alaskan Coastal Water apparent in July is not as clear

in August (Fig. 5). This may be due to much more limited data in August

in the Alaskan Coastal Current region after 1977.

Norton Sound is warmer in August in the latter period than prior to

1977. The Norton Sound data is well distributed over the years. Hamazaki

et al. (2005) found that Norton Sound benthic biomass increased after 1976.

Whether these ecosystem changes might be related to changes in temperature is unclear.

The region along the northern Siberian coast that showed some indication

of cooling in July exhibits warming in August. Again, limited data exist in

the post-1977 period, so the warming signal is heavily influenced by only a

few years of data.
8 Ladd and Overland Degrees C

July

Pre-1977

July

1977-2004

Difference

Figure 4: Objective maps of July SST pre-1977 (top), 1977–2004 (middle) and difference (middle–top).

Data used to create the objective maps are overlaid as circles.
Sea surface temperature in northern Bering and Chukchi seas 9 Degrees C

August

Pre-1977

August

1977-2004

Difference

Figure 5: As in Figure 4, for August.
10 Ladd and Overland Degrees C

September

Pre-1977

September

1977-2004

Difference

Figure 6: As in Figure 4, for September.
Sea surface temperature in northern Bering and Chukchi seas 11

5.3 September

Warming across the northern part of the region in September (Fig. 6) may

be due to changes in sea-ice extent. According to the Hadley Centre Sea

Ice dataset (Rayner et al., 2003), the northern edge of our region exhibited

>30% sea ice coverage during July–September prior to 1977. In the years

1977–2004, summer sea ice coverage in the region averaged 5–10%. Less sea

ice over the summer would allow more heat to be absorbed by the surface

waters.

Norton Sound and Kotzebue Sound both exhibit cooler conditions after

1976 (Fig. 6). Post-1977 Norton Sound data were dominated by 1985 data

while Kotzebue Sound was dominated by 1986 data. Cooling in Norton and

Kotzebue Sounds may indicate less transport of Alaskan Coastal Water in

September. However, August and September Yukon River discharge were

higher than average in 1985 and 1986. Nome air temperature data (Fig. 2)

show that September 1986 and 1987 were slightly cooler than average.

6. Temporal Variability in Bering Strait

The results discussed above have to be considered with caution, as the sampling in this region has not been temporally or spatially consistent. The

most consistently sampled part of the region is Bering Strait. Here, we focus on Bering Strait, comparing historical WOD05 data with more recent

transects.

Using all data in the WOD05 database, the properties of the eastern

(168.5–168◦W, 65.5–66◦N) and western (169.5–169◦W, 65.75–66.25◦N) sides

of Bering Strait can be examined. Surface temperatures (10-m average)

average greater than 7◦C in the eastern part of the strait and less than

4◦C in the western part of the strait in July–September (Table 1). The

range of temperature observations in eastern Bering Strait is large. The

coldest surface temperatures recorded in the eastern part of the pass were

less than 1◦C in early July 1985 while the warmest temperatures were greater

than 12◦C in August 1968. Part of that range is due to the lateral extent

of the warm Alaskan Coastal Current. The colder temperatures tend to

be those measured farther west. On the western side of the strait, the

temperature range is smaller. The coldest temperature recorded was –0.6◦C

in late September 1957, while the warmest surface temperature recorded was

almost 7.0◦C in August 1962. Examination of available Bering Strait data

shows no significant trends over the 20th century (Fig. 7). Thus, we cannot

reject the null hypothesis that the data are sampled from a single population

(i.e., no regime shifts). However, due to the temporal sparseness of data,

the possible existence of low-frequency variability or trends cannot be ruled

out.

In recent years (2004–2007), the Russian-American Long-term Census

of the Arctic (RUSALCA) program (http://www.arctic.noaa.gov/aro/

russian-american/) sampled across Bering Strait. These data are not in-
12 Ladd and Overland

West Bering Strait 

July 

August 

September 

0 

2 

4 

6 

8 

10 

12 

14 

1930 1940 1950 1960 1970 1980 1990 2000 2010 

July 

August 

September 

East Bering Strait 

0 

2 

4 

6 

8 

10 

12 

14 

1930 1940 1950 1960 1970 1980 1990 2000 2010

-1 

0 

1 

2 

3 

4 

5 

6 

7 

8 

9 

1930 1940 1950 1960 1970 1980 1990 2000 2010 

-1 

0 

1 

2 

3 

4 

5 

6 

7 

8 

9 

1930 1940 1950 1960 1970 1980 1990 2000 2010 

-1 

0 

1 

2 

3 

4 

5 

6 

7 

8 

9 

1930 1940 1950 1960 1970 1980 1990 2000 2010 

0 

2 

4 

6 

8 

10 

12 

14 

1930 1940 1950 1960 1970 1980 1990 2000 2010 

Figure 7: Time series showing SST (◦C) for all available data in the western Bering Strait (169.5–169◦W,

65.75–66.25◦N) on the left and the eastern Bering Strait (168.5–168◦W, 65.5–66◦N) on the right. Historical

data from WOD05 represented by small diamonds; RUSALCA data represented by squares (August 2004),

triangles (August 2005), large diamonds (August 2006) and circles (September 2007).

cluded in the WOD05 database, nor in the statistics reported in Table 1. In

August 2004, only one cast was sampled in the eastern region defined above.

The 10-m average temperature on that cast was 12.9◦C, warmer than any

previous measurements in the database (Fig. 7). This is consistent with

summer bottom temperatures from a mooring in the eastern Bering Strait.

Woodgate et al. (2006) show bottom temperatures at mooring A4 that were

∼2◦C warmer in 2004 than measured the three previous years at that site.

The three RUSALCA casts in the western region of the strait were within

the range of variability seen in the historical data (Fig. 7).

In 2005, temperatures in both the eastern and the western regions were

near average. In 2006, the casts on the western side of the Strait were warmer

than the previous observed temperature range, while the eastern side of the

Strait was near (or slightly below) the mean of previous observations. The
Sea surface temperature in northern Bering and Chukchi seas 13

Table 1: Comparison of sea surface temperature on the eastern and western sides of Bering Strait.

Western side of Strait Eastern side of Strait

(169.5–169◦W, 65.75–66.25◦N) (168.5–168◦W, 65.50–66.00◦N)

Mean St. Dev. Range No. of casts Mean St. Dev. Range No. of casts

July 2.7 1.3 0.5–6.0 53 7.3 1.9 0.9–10.5 89

August 3.7 1.7 0.4–7.0 81 8.4 1.6 3.4–12.1 220

September 3.6 1.6 –0.6–5.7 24 7.0 1.8 2.5–10.9 69

warmest 10-m average temperature recorded in August 2006 in the western

region of Bering Strait was 8.4◦C, ∼1.4◦C higher than the previous observed

high temperature.

The 2007 RUSALCA cruise was completed in early September. Temperatures ranged from 4.0–6.0◦C in the western strait and 9.6–10.6◦C in the

eastern strait. These temperatures are at the warm end (but not outside)

of previously observed range of temperatures in the east. In the west, the

warmest temperatures observed in 2007 were ∼0.3◦C warmer than previously observed (prior to 2006).

A transect across Bering Strait taken 5 September 1880 (and not included

in the WOD05 database) shows surface temperatures of 2.6–2.8◦C on the

western and 8.3–8.9◦C on the eastern side of the strait (Fig. 8) (Dall, 1882).

These temperatures are lower than average on the eastern side and higher

than average on the western side compared to the 20th century climatology

but within one standard deviation of the mean (Table 1), and thus are not

inconsistent with the 20th century SST climatology.

7. Discussion and Summary

We have addressed regional changes for the northern Bering and Chukchi

Seas around the 1976 regime shift, and 20th century time series in the vicinity

of Bering Strait.

While surface air temperatures show a strong warming signal after 1977,

high variability in this region and sparse oceanic sampling make it impossible to draw robust conclusions regarding low-frequency variability in SST.

Sampling has not been consistent spatially or temporally. Thus, observed

changes in SST surrounding the 1977 regime shift have to be interpreted with

caution. Some observed changes were relatively strong and spatially consistent, suggesting real changes. In July, the region influenced by the Alaskan

Coastal Current was warmer after 1977, while the region over Herald Shoal

was colder. This pattern did not carry into August and September. Norton

Sound data shows post-1977 warming in August, while both Norton and

Kotzebue Sounds exhibit cooling in September. The lack of similar patterns

in the 3 months may be due to real intraseasonal variability in oceanic conditions possibly due to seasonality of Yukon River discharge (July discharge

is significantly greater than August or September discharge). However, it

could be purely due to insufficient data.
14 Ladd and Overland

Figure 8: Temperature transect (◦F) across Bering Strait taken in September 1880 (bottom) along with

location of transect (top). From Dall (1882).
Sea surface temperature in northern Bering and Chukchi seas 15

Given the data at hand, we cannot conclude that the northern Bering/

Chukchi Sea region shows decadal-scale or regime-shift variability in SST

compared to the hypothesis that all measurements for the 20th century come

from a single population. However, we also cannot say conclusively that no

decadal or longer timescale variability existed. The warmest temperatures

ever measured in the eastern Bering Strait were measured in 2004 and the

warmest temperatures measured in western Bering Strait were observed in

2006, providing evidence that we may be seeing a warm period in the 21st

century superimposed on substantial interannual variability. Model results

suggest that the influence from the anthropogenically forced trend in SST

will be as large as the natural variability in North Pacific SST by 2030–2050

(Overland and Wang, 2007). Thus, we would expect to see additional temperature measurements outside of the range observed thus far. In contrast,

data from the end of the little ice age (1880) is not inconsistent with the

20th-century climatology.

To have a baseline for comparison of potential future changes in the

northern Bering and Chukchi Seas, it was important to assemble all previous

data and assess how far the previous record can be characterized, given data

gaps. Sampling from a single population is as far as we can reasonably go in

identifying the 20th-century climate structure for the Bering Strait region.

The paper points out the importance of obtaining every scrap of historical

data; even single measurements in single years help to determine the range of

interannual variability. These data are golden for climate analyses. Further,

the importance of continuing regular observations, consistent in location and

month for every year, is self evident.

8. Acknowledgments

We gratefully acknowledge support from the NOAA Arctic Research of the

Climate Program Office. Tom Weingartner and Seth Danielson kindly provided the RUSALCA data. This research is contribution EcoFOCI-0698

to NOAA’s Ecosystems and Fisheries-Oceanography Coordinated Investigations and PMEL contribution 3263.
16 Ladd and Overland

9. References

Ahln ̈as, K., and G.R. Garrison (1984): Satellite and oceanographic observations of

the warm coastal current in the Chukchi Sea. Arctic, 37, 244–254.

Coachman, L.K., K. Aagaard, and R.B. Tripp (1975): Bering Strait: The regional

physical oceanography. University of Washington Press, Seattle, WA, 172 pp.

Dall, W.H. (1882): Report on the currents and temperatures of Bering Sea and

adjacent waters. In Report of the superintendent of the U.S. Coast and Geodetic

Survey showing the progress of the work during the fiscal year ending June 1880,

Appendix 16, United States Coast and Geodetic Survey, 297–341.

Grebmeier, J.M., J.E. Overland, S.E. Moore, E.V. Farley, E.C. Carmack, L.W.

Cooper, K.E. Frey, J.H. Helle, F.A. McLaughlin, and S.L. McNutt (2006): A

major ecosystem shift in the northern Bering Sea Science. Science, 311, 1461–

1464, doi: 10.1126/science.1121365.

Hamazaki, T., L. Fair, L. Watson, and E. Brennan (2005): Analyses of Bering

Sea bottom-trawl surveys in Norton Sound: absence of regime shift effect on

epifauna and demersal fish. ICES J. Mar. Sci., 62, 1597–1602.

Johnson, D.R., T.P. Boyer, H.E. Garcia, R.A. Locarnini, A.V. Mishonov, M.T.

Pitcher, O.K. Baranova, J.I. Antonov, and I.V. Smolyar (2006): World Ocean

Database 2005 Documentation. , edited by S. Levitus, NODC Internal Report

18, U.S. Government Printing Office, Washington, D.C., 163 pp.

Kessler, W.S., and J.P. McCreary (1993): The annual wind-driven Rossby wave in

the subthermocline equatorial Pacific. J. Phys. Oceanogr., 23, 1192–1207.

Martin, S., and R. Drucker (1997): The effect of possible Taylor columns on the

summer ice retreat in the Chukchi Sea. J. Geophys. Res., 102, 10,473–10,482.

Maslanik, J., S. Drobot, C. Fowler, W. Emery, and R. Barry (2007): On

the Arctic climate paradox and the continuing role of atmospheric circulation in affecting sea ice conditions. Geophys. Res. Lett., 34, L03711, doi:

10.1029/2006GL028269.

Nghiem, S.V., I.G. Rigor, D.K. Perovich, P. Clemente-Col ́on, J.W. Weatherly, and

G. Neumann (2007): Rapid reduction of Arctic perennial sea ice. Geophys. Res.

Lett., 34, L19504, doi: 10.1029/2007GL031138.

Overland, J.E., J.M. Adams, and N.A. Bond (1999): Decadal variability of the

Aleutian low and its relation to high-latitude circulation. J. Climate, 12, 1542–

1548.

Overland, J.E., and A.T. Roach (1987): Northward flow in the Bering and Chukchi

Seas. J. Geophys. Res., 92, 7097–7105.

Overland, J.E., and M. Wang (2007): Future climate of the North Pacific Ocean.

Eos Trans. AGU , 88, 178, 182.

Paquette, R.G., and R.H. Bourke (1981): Ocean circulation and fronts as related

to melt-back in the Chukchi Sea. J. Geophys. Res., 86, 4215–4230.
Sea surface temperature in northern Bering and Chukchi seas 17

Polyakov, I., L. Timokhov, E. Hansen, J. Piechura, W. Walczowski, V. Ivanov,

H. Simmons, E. Fahrbach, J. H ̈olemann, M. Steele, R. Pickart, L. Fortier,

U. Schauer, A. Beszczynska-M ̈oller, N.P. Holliday, I. Dmitrenko, R. Dickson, J.-C. Gascard, and C. Mauritzen (2007): Observational program tracks

Arctic Ocean transition to a warmer state. Eos Trans. AGU , 88, 398, doi:

10.1029/2007EO400002.

Polyakov, I.V., R.V. Bekryaev, G.V. Alekseev, U.S. Bhatt, R.L. Colony, M.A. Johnson, A.P. Maskshtas, and D. Walsh (2003): Variability and trends of air temperature and pressure in the maritime Arctic, 1875–2000. J. Climate, 16, 2067–

2077.

Rayner, N.A., D.E. Parker, E.B. Horton, C.K. Folland, L.V. Alexander, D.P. Rowell, E.C. Kent, and A. Kaplan (2003): Global analyses of sea surface temperature, sea ice, and night marine air temperature since the late nineteenth century.

J. Geophys. Res., 108(4407), doi: 10.1029/2002JD002670.

Roach, A.T., K. Aagaard, C.H. Pease, S.A. Salo, T. Weingartner, V. Pavlov, and

M. Kulakov (1995): Direct measurements of transport and water properties

through Bering Strait. J. Geophys. Res., 100, 18,443–18,457.

Savelieva, N.I., I.P. Semiletov, L.N. Vasilevskaya, and S.P. Pugach (2000): A climate shift in seasonal values of meteorological and hydrological parameters for

Northeastern Asia. Prog. Oceanogr., 47, 279–297.

Shimada, K., E.C. Carmack, K. Hatakeyama, and T. Takizawa (2001): Varieties

of shallow temperature maximum waters in the Western Canadian Basin of the

Arctic Ocean. Geophys. Res. Lett., 28, 3441–3444.

Steele, M., W. Ermold, and J. Zhang (2008): Arctic Ocean surface warming trends over the past 100 years. Geophys. Res. Lett., 35, L02614, doi:

10.1029/2007GL031651.

Steele, M., J. Morison, W. Ermold, I. Rigor, M. Ortmeyer, and K. Shimada (2004):

Circulation of summer Pacific halocline water in the Arctic Ocean. J. Geophys.

Res., 109, C02027, doi: 10.1029/2003JC002009.

Stroeve, J., M. Serreze, S. Drobot, S. Gearheard, M. Holland, J. Maslanik,

W. Meier, and T. Scambos (2008): Arctic sea ice extent plummets in 2007.

Eos Trans. AGU , 89, 13–14.

Weingartner, T.J., S. Danielson, Y. Sasaki, V. Pavlov, and M. Kulakov (1999):

A wind- and buoyancy-forced Arctic coastal current. J. Geophys. Res., 104,

29,697–29,713.

Woodgate, R.A., K. Aagaard, J.H. Swift, K.K. Falkner, and W.M. Smethie (2005a):

Pacific ventilation of the Arctic Ocean’s lower halocline by upwelling and diapycnal mixing over the continental margin. Geophys. Res. Lett., 32, L18609,

doi: 10.1029/2005GL023999.

Woodgate, R.A., K. Aagaard, and T.J. Weingartner (2005b): A year in the physical

oceanography of the Chukchi Sea: Moored measurements from autumn 1990–

1991. Deep-Sea Res. I, 52, 3116–3149.

Woodgate, R.A., K. Aagaard, and T.J. Weingartner (2006): Interannual changes in

the Bering Strait fluxes of volume, heat and freshwater between 1991 and 2004.

Geophys. Res. Lett., 33, L15609, doi: 10.1029/2006GL026931.