by David Klein, John Walsh, and Martha Shulski
Caption: Location of Saint Matthew Island
In recent years the media has focused considerable attention on the impact of extreme weather events, such as coastal storms, regional flooding, and drought, on humans, their homes, their infrastructure, and their agriculture. But little attention has been paid to the impact such weather events has on native wildlife species. Studies show that as the Earth's climate warms, rates of extinction are increasing, habitats are changing and shifting, and invasive species are moving in and creating more competition for local resources. Such stresses are compounded when an extreme weather event occurs. An event that occurred in the winter of 1964 provides a case study for the problem and shows that when an unstable wildlife population is confronted with extreme weather, the results can be devastating.
Caption: The island of Saint Matthew, shown here in 1966, is located about 200 miles to the west of Alaska's Yukon Delta. It is about 115 square miles and is dominated by a maritime climate influence.
The island of Saint Matthew is located about 200 miles to the west of Alaska's Yukon Delta. With an area of about 115 square miles, the island is a part of the Alaska Maritime National Wildlife Refuge and has no permanent human inhabitants. The terrain is dominated by low mountains and intervening lowlands under a maritime climate influence with tundra vegetation. During winter, the Arctic pack ice can encompass the island.
During World War II, the United States Coast Guard introduced reindeer (Rangifer tarandus) to Saint Matthew Island as an emergency food supply for military personnel, but abandoned both the island and the reindeer when the war ended. The reindeer were left to increase in the absence of natural predators, and the resulting reindeer population explosion led to over-exploitation of the limited resources of the island. From the original 29 animals introduced in 1944, the reindeer population had increased to a staggering 6,000 animals by the summer of 1963. However, scientists scouting the island a few years later found only 42 of them alive. An exceptionally cold period that included violent winter storms, heavy snow, and bitter wind chills in late January and early February of 1964 was found to be the culprit accounting for the mass die-off of the reindeer.
Caption: 6,000 reindeer lived here on St. Matthew Island in the Bering Sea in 1963. By the 1980s, zero reindeer remained.
Several decades later, with climate change presenting an ever growing challenge for scientists studying wildlife and weather, wildlife biologist David Klein of the International Institute of Arctic Biology joined forces with climatologists John Walsh of the International Arctic Research Center at the University of Alaska Fairbanks and Martha Shulski of the School of Natural Resources at the University of Nebraska, Lincoln, to reconstruct the weather events of early 1964 in the Bering Sea to see what insight they could glean from the reindeers' demise. Not only is the extreme weather event of interest from a climatological perspective, but the scenario also highlights the vulnerability of wildlife populations existing on islands or other fractured and isolated habitats where mobility is not an option for survival when extreme weather events might occur. The analysis used data recorded at Saint Paul Island, the closest weather station 200 miles to the south of Saint Matthew, as well as reanalyzed fields of key weather variables that had recently become available through reanlysis by the National Centers for Environment Prediction (NCEP).
Extreme Weather of the 1964 Winter
The extreme weather affecting Saint Matthew Island in the winter of 1964 can be viewed in two timeframes: a two-month period of unusual cold and storminess from late January through mid-March; and a series of particularly strong storm events—by some measures, unique in the past 60 years of weather records—that affected the northern Bering Sea region in the first days of February 1964. The storms were associated with a large-scale circulation anomaly pattern over the North Pacific Ocean. While the network of observing stations providing measurements on the ground from the North Pacific and the Bering Sea is sparse—and was even more sparse in 1964—the scientists were able to draw upon the atmospheric reanalysis to reconstruct the weather of this time period and to place the 1964 event into a 60-year context. In their examination of the winter of 1963–1964, the scientists paid particular attention to the data on sea level pressure, surface air temperature, and surface winds from the NCEP reanalysis. Data were culled from available surface weather stations, ship and buoy reports, rawinsondes, aircraft reports and, from the 1970s onward, satellite-derived vertical profiles of the atmosphere.
Caption: An occasional skull or antler was all that remained of the St. Matthew reindeer in summer 2005.
For December 1963, the monthly average sea level pressure field from the NCEP reanalysis shows that a broad region of negative pressure anomalies (as large as 12 mb) was located south of the Aleutians in the North Pacific. The negative pressure anomalies moved north to the southern coast of Alaska in January. This pattern indicates the likelihood of enhanced storminess from the Aleutians to the southern Alaskan coast to the Alaskan Panhandle. Together with the positive pressure anomalies over northeastern Asia, the resulting pressure gradient points to unusually strong northerly winds that brought abnormally cold air into the westernmost Bering region and adjacent Russia. This pattern shifted northward with a strengthening of the positive pressure anomalies over the Russian Far East in February, continuing the influx of cold Arctic air into the Bering Sea and shifting it eastward to the Saint Matthew Island region. The anomaly pattern weakened in March, when the extreme winter conditions began to moderate, although the extensive sea ice cover that developed during February helped to maintain the extremely cold conditions around Saint Matthew Island throughout March.
The corresponding fields of surface air temperature show that the northern Bering Sea experienced temperatures that were 18°F to 22°F below normal in February at some locations in the northern Bering Sea, making it one of the three coldest Februaries (comparable to 1976 and 1984) in the 60-year period from 1948–2007. The extremely cold conditions were present to the west and north of the Bering Sea in January 1964 and abnormal cold (anomalies of −7 to −11°F) continued in the eastern Bering Sea into March of that year.
The bitter cold and unrelenting storms that pummeled Saint Matthew Island in the winter of 1964 would have put any living creature to the test, but for the reindeer on the island that winter, the weather proved far more deadly. But what exactly caused the incredibly high death rate of the reindeer? One important factor was the higher snow depths and hard crusts on the snowpack that meant the reindeer were virtually prevented from obtaining any of their already depleted food resources, which still remained beneath the snow. From January 1 to March 31, the average snow depth was 19 inches on Saint Paul, far above the normal average snow depth of 5 inches. In addition, the depth of snow on the ground remained above 20 inches from February 1 to April 9, and it did not melt entirely until May 4.
The cold air temperatures and associated extreme wind chill were additional metabolic stresses on the already nutritionally stressed reindeer. Mean daily temperature departures at Saint Paul were in the range of −4°F to −18°F during the first 2 weeks of February. Wind speeds for the end of January and early February show several peaks with the highest values of 67 mph on the evening of January 4. Winds at the Saint Paul airport remained high, with daily averages of 20–45 mph throughout the period January 30 to February 7, with only a brief respite on February. 3 Strong winds along with high rates of precipitation resulted in a considerable reduction in visibility as hourly observations were less than half a mile during the first week of February.
From 6,000 reindeer entering the winter of 1964, only 42 reindeer survived the storm in early February and the remaining winter. These included 41 females and 1 abnormal and non-viable male. No breeding and therefore no recruitment of new animals occurred after the massive die-off, and the female reindeer subsequently declined to extirpation. Among the skeletons of females that had been pregnant when the die-off occurred, the stage of development of the fetal remains indicated that most of the pregnant females had died about the time of the storms or shortly thereafter.
Large anomalies on the monthly and seasonal timescales are difficult to attribute to gradual changes in the radiative energy that drives climate, such as those associated with increasing concentrations of greenhouse gases. As a result, the scientists concentrated their attention on more transient influences on climate, such as those associated with volcanic eruptions. They found one event that could have played a major role in the atmospheric patterns during the winter of 1964. That winter followed the eruption of the volcano Agung in Indonesia during February of 1963. When compared with cold seasons that followed other significant volcanic events, the atmospheric circulation anomalies at sea level and aloft (500 mb) during the January- February period of 1964 show some similarities—as well as some differences—relative to the circulation anomalies in January-February of 1983 and 1992, the winters following the eruptions of the El Chichón in Mexico and Mount Pinatubo in the Phillipines, respectively. After each eruption, upper-air pressures were below normal over Alaska and the Bering Sea. The normal pattern of pressures and winds was displaced toward the equator over at least some portion of the North Pacific-Alaska region in each year. However, large northward displacements were found over eastern Russia and the central North Pacific in 1964 but not in 1983 and 1992, implying that natural variability (unrelated to volcanoes, greenhouse gases, or factors influencing radiational energy fluxes) was also likely an important factor to the circulation pattern of early 1964.
The strongest storm event occurred during the first several days of February 1964, when a surface low pressure system that originated over the warm waters of the western Pacific Ocean tracked eastward from Japan on January 29. The central pressure of this extratropical cyclone gradually decreased from 995 mb offshore of Japan on January 29 to 970 mb near the International Dateline on January 31. As a low pressure center intensifies, wind speeds increase in response to the stronger contrasts of pressure in the vicinity of the storm. In this case, the intensification of the low then accelerated, and the storm subsumed a pre-existing weaker low over the Aleutians, where the central pressure decreased to 957 mb on February 1. Such pressures are typical of Category 3 hurricanes. The low maintained this intensity for 12 hours and tracked over the Aleutians and Bristol Bay before slowly weakening over the topography of south-central Alaska on February 2–3.
Caption: A group of bull reindeer on Saint Matthew Island at the height of the population in July 1963.
The track and intensity of the low were such that Saint Matthew Island was in the storm's northwest quadrant during its peak-intensity phase on February 1. At the same time, the pressure over the Russian Far East was extremely high (in excess of 1050 mb). The pressure difference between the intense cyclone and the Siberian high at 06 UTC on February 1 exceeded 100 mb—the largest pressure gradient between these 2 locations in the entire 60-year period of the reanalysis. This record pressure difference led to extremely strong northerly winds that brought bitterly cold arctic air over Saint Matthew Island. Winds peaked at 63 mph, while temperatures ranged from −9°F to −27°F from February 1 to February 7. The wind chill temperature dropped to −58°F and remained colder than −40°F almost continuously during the week of February 1–7. A series of additional storms over the next 6 weeks led to wind chills below −40°F for an additional 90 hours from February 10–20 and for 156 hours from March 1–16. The lowest wind chill reading, −71.5°F, was reached on March 13 with an air temperature of −34°F and a wind of 30 mph.
Because there was no weather reporting station on or near Saint Matthew Island at this time, investigators relied on weather data from the nearby Saint Paul Island airport, which showed that this sequence of storms was indeed record-breaking for the Bering Sea region. Two record daily totals occurred during this event: the highest 24-hour snowfall for the month of February on 4 February 1964 (13 inches) and the highest all time 24-hour snowfall total on 30 January 1964 (14 inches). In addition, monthly snowfall and precipitation totals for February of 56 inches (590 percent of normal) and 6.5 inches (520 percent of normal), respectively, are the current record-holders. For the 1963–1964 season on the whole, Saint Paul received 140 inches of snow, which is 245 percent of normal and is the record highest seasonal total. Comparison of seasonal snow totals to Nome (73 percent of normal) and Bethel (85 percent of normal) on the Bering Sea coast reveal that the extreme snow amount at Saint Paul was a regional phenomenon.
An Extreme Case
In the summer of 1963, the reindeer population had reached its peak density on the island. The stage had been set for the Saint Matthew Island reindeer to undergo a major population decline following the extreme over-exploitation of lichens, the major component of their winter diet. The severity of the crash die-off that led to the extirpation of the population resulted from the deadly combination of lack of available food and extreme stress from the wintery weather. Although the reindeer of Saint Matthew Island are not the only reindeer population to be introduced to an area, reach peak population levels, and then decline because of over-exploitation of resources, they did experience an unprecedented level of die-off as a direct result of the extreme weather.
On islands isolated from other land areas, normally wide-ranging mammals, such as reindeer and caribou, do not have the option for migration or dispersal when they are stressed by food limitations in their seasonal environments. The species Rangifer tarandus, which includes caribou and reindeer, and Ovibos moschatus, the muskox, are the only two extant ungulate species with adaptations that have enabled them to survive under the harsh climatic extremes of the Arctic. Nevertheless, throughout the Arctic their populations have waxed and waned in response to changes in conditions within their local environments. Extreme weather events, such as winter storms that result in icing of the snow surface or of the vegetation, thus limiting access to food, are believed responsible for periodic extirpation of Peary caribou (R. t. pearyi) and muskoxen on some islands in the Canadian Arctic. Similarly, the extinction of caribou (R. t. eogroenlandicus) in northeast Greenland around 1900 is believed to have been caused by excessive winter snow accumulation and icing during a period of absence of coastal sea ice.
Caption: Map showing location of Saint Matthew and Saint Paul islands in the Bering Sea and their positions on the Beringian continental shelf. The growth of the reindeer population on Saint Matthew (insert) is shown from the introduction of the population peak, followed by the die-off.
Caption: The fate that befell the reindeer of Saint Matthew Island provides a chilling warning for animal populations struggling to cope with a changing climate.
What about the possibility of future cases like this one? Global climate models project a decrease of pressure in the Bering Sea region during the twenty-first century, implying an increased frequency and/or severity of winter storm events, as well as an increase of winter snowfall. In comparison with changes in climatic means, an increased frequency and severity of extreme weather events could pose a more immediate threat to animal species that are at risk. When threatened or endangered species are restricted to islands or fractured habitats where dispersal is not an option, their vulnerability to extinction is greatly enhanced. Unfortunately, the disaster that befell the reindeer of Saint Matthew Island provides a case study for population declines that, in the coming years, could prove to be an early warning of what is to come.