Cook expedition

In 1772–75, Captain James Cook led a British expedition to discover the hypothesized Great Southern Continent in the high latitudes of the Southern Hemisphere. This was the first major expedition to remain in the Southern Ocean for an extended period and the first to cross the Antarctic Circle. Although many earlier expeditions had encountered outlying icebergs, few had reached the main ice pack and those had all been hindered in recording ice edge locations by the difficulties prior to the 1760s of obtaining longitudes accurately from sea. During the 1772–75 expedition, Cook spent much of each austral summer poleward of 50°S, circumnavigated the undiscovered Antarctic continent, and recorded the position of the ice edge at several locations, obtaining longitudes with the help of the newly-devised seaworthy chronometer of John Harrison (Cook, Reference Cook, Strahan and Cadell1777).

Table I.

Ice Edge Locations Recorded by Cook (1777)

When Cook’s ice edge locations (Table I) are compared with ice edge locations during the ESMR period 1973–76, his December 1772 observations from the eastern Weddell Sea stand out as particularly noteworthy. These observations suggest a significantly heavier ice cover than occurred at the same time of year in the 1973–76 period. This is true especially of his 14–18 December observations in the vicinity of 55°S, which are 2–8° farther north than the mid-December ice edge at the same longitudes in 1973–76. On the other hand, it is clear from Cook’s notes for the succeeding days, as he traveled southward in the absence of ice, that the ice encountered on 14–18 December was probably either an isolated field of ice or part of a tongue of ice lying well north of the rest of the ice at the same longitude. The possibility of an ice tongue is heightened by the fact that Cook’s 31 December 1772 observation at 60°21’S, 13°13’E is of a sea-ice edge to his north, not his south. These observations suggest the spring/summer Weddell Sea ice tongue frequently found in satellite data (e.g. Zwally and others, Reference Zwally, Comiso, Parkinson, Campbell, Carsey and Gloersen1983), although the timing and placement of the observations suggest a lag in the melt season of up to several weeks behind the timing for the 1970s. It should be noted that Cook’s 26 December 1772 observation at 58°31’S, 27°37’E is of ice bands, not a solid ice pack.

Cook’s observations around the remainder of the continent do not confirm the heavy ice cover (relative to that in the 1970s) found by him in the eastern Weddell Sea. His observations in the Ross Sea suggest slightly less ice than in the 1970s, and his observations in the Amundsen Sea at 71°10’S, 106°54’W and off the Kronprins Olav Kyst at 67°15’S, 39°35’E suggest ice edge locations within the range of interannual variability found from the ESMR data. The Weddell Sea/Ross Sea contrast is of interest, but so far remains unexplained.

Table II.

Ice Edge Locations Recorded by Bellingshausen (1831)

Bellingshausen expedition

In 1819–21, Captain Thaddeus Bellingshausen led a Russian expedition to explore the south polar waters. Bellingshausen circumnavigated the Antarctic continent, remaining south of 60°S for over half the distance and traveling along the ice edge for several stretches during January-February 1820 and December 1820-January 1821. He spent the intervening winter period in the South Pacific (Bellingshausen, Reference Bellingshausen1831), as had Cook (Reference Cook, Strahan and Cadell1777) during his voyages. Bellingshausen’s discoveries west of the Antarctic Peninsula led to the naming of the Bellingshausen Sea.

Comparison of Bellingshausen’s ice edge locations (Table II) with the ESMR satellite record reveals most of Bellingshausen’s observations to fall within the range of ice edge locations found in 1973–76. A prominent exception occurs on 21 January 1820, when Bellingshausen records sea ice at 59°36’S, 15°02’W. This is far north (almost 10° of latitude) of the position of the ice edge in late January in the 1970s; and yet Bellingshausen’s description of an ice field extending “from northeast to southsouthwest, in the midst of which were wedged a large number of large flat icebergs” (Bellingshausen, Reference Bellingshausen1831) definitely suggests the presence of sea ice, not just icebergs and iceberg debris. Further, the consistency of his recorded locations on preceding and succeeding days eliminates the likelihood of a major error in recording latitude. It is conceivable that Bellingshausen encountered a small ice field well distant from the main ice pack. Otherwise it appears that at this longitude the ice cover in January 1820 was much heavier than that in January 1973–76.

The four other ice edge locations listed in Table II as falling outside the 1973–76 range were all outside that range by less than 1° of latitude. This includes the 18 February 1820 Weddell Sea observation of less ice than in 1973–76, the two December 1820 Ross Sea observations of more ice than in 1973–76, and the 10 January 1821 Amundsen Sea observation of more ice than in 1973–76. The low ice cover indicated in the Weddell Sea on 18 February 1820 and the 28 January 1820 and 2 February 1820 ice edge locations (which fall within the 1973–76 range) support the conjecture that the observation of ice at a particularly low latitude on 21 January 1820 either was of a separated field of ice distant from the main ice pack, or signified an unusually late retreat of the Weddell Sea ice tongue. A reviewer pointed out the possibility that the heavy ice cover on 21 January, although an isolated observation, could be related to the widespread cooling following the 1815 eruption of Tambora. It would be interesting to examine such a connection with data from the years prior to and immediately following the eruption.

Table III.

Ice Edge Locations Recorded During the Wilkes Expedition (from Bertrand, 1971)

Wilkes expedition

The United States Exploring Expedition of 1838–42, led by Lieutenant Charles Wilkes, was a four-year, wide-ranging expedition of exploration in many regions of the world’s oceans, with exploratory parties sent inland at numerous coastal locations. The expedition included two major excursions into Southern Ocean waters, the first in February and March of 1839 and the second in January and February of 1840. During the latter period, Wilkes and his subordinates journeyed for 1500 miles along the edge of the pack ice south of Australia, off what has become known as Wilkes Land (Bertrand, Reference Bertrand1971). The ice edge locations listed in Table III are from several ships taking part in the Wilkes expedition.

Wilkes found a heavier ice cover in the Amundsen Sea in March 1839 than existed in March of 1974–76 (March 1973 data are not available), with the three Amundsen Sea ice edge locations listed in Table III falling outside the latitude range of the 1974–76 ice edges at the respective longitudes by 1–2.5° of latitude. The two Ross Sea locations listed in Table III, for mid-January 1840, also suggest a heavier ice cover than at the same time of year in 1973–76, in this case by 1–1.5° of latitude. However, as the Wilkes expedition traveled westward from the Ross Sea, their ice edge locations tended to be within the 1973–76 range or slightly poleward (by less than 1° of latitude) of the 1973–76 range. The one exception to this in Table III, the final entry, concerns an ice edge location equatorward of the 1973–76 range by less than 0.5° of latitude.

[It should be noted that the source used for Wilkes (Bertrand, Reference Bertrand1971), in contrast to those used for Cook, Bellingshausen, and Ross, is a secondary source, not the direct records of Wilkes or of anyone in his expedition. Many more ice edge locations are likely to be found by examining the various primary sources from Wilkes and his colleagues.]

Ross expedition

The 1839–43 expedition led by Sir James Clark Ross was a British scientific expedition to measure magnetic direction and intensity in high southern latitudes and to attempt to reach the South Magnetic Pole. As a part of the latter effort, Ross sailed through the later-named Ross Sea and explored along the adjacent Antarctic coastline and Ross Ice Shelf in January, February, and March of 1841 (Ross, Reference Ross1847). Although Ross returned to the Ross Sea the following summer and then attempted to penetrate the sea ice of the Weddell Sea in 1843, it is his Ross Sea exploration of 1841 which is discussed here. Because of sailing through rather than along the ice pack, Ross’s mentions of outer ice edge locations during the Ross Sea portion of his voyage are fewer than those of Bellingshausen or Wilkes. However, Ross gives more information on local sea-ice conditions and the existence or non-existence of open water areas within the ice pack.

Ross encountered the ice edge late in the morning on 1 January 1841, and was just within the ice pack at noon, when his location was 66°32’S, 169°45’E. This is within the 1973–76 range of outer ice edge locations on 1 January at that longitude. Similarly, Ross was somewhat within the pack on 5 and 6 January when at 66°55’S, 174°34’E and 68°17’S, 175°21’Ε, respectively, and both these locations are within the 1973–76 range of ice distributions for 5 and 6 January. Ross, still traveling southward, reached open water early on 9 January 1841, continuing in open water at noon, when his location was 69°15’S, 176°15’E. This location was also open on 9 January in both 1974 and 1975, in the former case as part of an embayment reaching southward to the Ross Ice Shelf and in the latter case as part of a large Ross Sea polynya. In 1973 there was ice in this location but only as part of a band separating a large Ross Sea polynya to the south from the open water to the north. As Ross explored the southern Ross Sea for the remainder of January and February 1841, his several indications of where he encountered ice and where he encountered open water are all consistent with 1973–76 conditions, generally indicating more ice than in 1975 but less ice than in 1976.

In March 1841 Ross traveled along the ice edge off Victoria Land, proceeding westward from 167°E to 142°E. His recorded ice edge locations along this route, between 68° and 65°S from 167°E to 162°E and between 63° and 65.2°S from 162°E to 142°E, predominantly fall within the range of ice edge locations for March 1974–76. Hence the sea-ice locations found by Ross in the Ross Sea vicinity during the first three months of 1841 suggest ice distributions similar to those in the 1970s.

Sealers and whalers

Many sealers and whalers in the late 18th and entire 19th centuries spent considerable time in Southern Ocean waters, and some made important exploratory voyages, partly in search of better sealing grounds. Among these were the Englishman James Weddell, who in 1822 sailed as far south as 74°15’S in the later-named Weddell Sea, and the American Nathaniel B. Palmer, who explored along the Antarctic Peninsula in the 1820s and 1830s, leading to the naming of Palmer Land. The logbooks of many of the sealing expeditions are available (some sources are given in Bertrand, Reference Bertrand1971), and a careful study of them could perhaps yield valuable information for climate studies. However, there are difficulties with many of these records, and for two reasons in particular they are not included in this study. The first reason lies in the frequent failure of many whalers and sealers to record accurate locations. This failure was often quite deliberate, the purpose being to hinder competitors from relocating select whaling or sealing grounds (Bertrand, Reference Bertrand1971). The second reason relates to a failure not of the whalers and sealers but of the satellite data being used for comparisons. Many of the whaling and sealing expeditions concentrated efforts amongst the islands of the Antarctic Peninsula or elsewhere in the near vicinity of land. The 30 km resolution of the satellite data makes it inappropriate for detailed studies in near-shore regions, where land contamination confounds the interpretation of the satellite data.

Summary

The ice edge locations mentioned in the various expedition reports discussed here do not indicate a strong Little Ice Age signal when compared with the ice edge locations found at the same times of year in the four-year period in the 1970s having satellite data coverage from the Nimbus 5 ESMR. In December 1772 Cook found a more extensive ice cover in the eastern Weddell Sea than appeared in December 1973–76, but a year later he found a somewhat less extensive ice cover in the Ross Sea than existed in December 1973–76. One of the ice edge locations given by Bellingshausen is well outside the 1973–76 range, suggesting a particularly extensive Weddell Sea ice cover on 21 January 1820, but that was an isolated instance preceded and succeeded by several Weddell Sea observations of ice edge locations within the 1973–76 range. Wilkes’s Amundsen Sea ice edge locations in March 1839 and Ross Sea ice edge locations in January 1840 suggest a somewhat more extensive ice cover than in March 1974–76 and January 1973–76 respectively, and these might be usable in supporting an hypothesis of a weak Little Ice Age signal, especially if bolstered by additional data. However, neither Wilkes’s observations along the Wilkes coast in 1840 nor Ross’s observations in the Ross Sea and off Victoria Land in 1841 suggest more extensive ice conditions than in the 1970s. Hence, although a few observations from these expeditions suggest more extensive ice coverage than in the ESMR years 1973–76 (and a few observations suggest less extensive coverage), there is no clear-cut evidence of significantly more extensive ice overall. The evidence instead suggests ice conditions generally not far different from those in the 1970s.