Across Atlantic Ice

by Dennis J. Stanford

  Although pine pollen is abundant over most of unglaciated eastern North America, only in the southern forests were pines the dominant trees. The LGM piney woods, along with various temperate hardwoods, extended to at least 35° north latitude. The Florida Peninsula had open parkland with warm-temperate species of conifers. This environment may have extended along the Gulf Coast.

  Fossils are rarely preserved in eastern North America because of the acidic soils. In locations where fossils are preserved, assemblages include animals known as disharmonious faunas that don’t normally live in the same environment, indicating a mix of open parklands and forest environments. In general, the fossil remains of major big game species include caribou and musk ox, which are found on the upland tundra zone. Mammoth and mastodon are found throughout most of the unglaciated regions, along with white-tailed deer, bison, and horse. There is a surprising variety of smaller mammals that no longer live side by side in today’s world. The fact that some of them required open grassland and others were forest dwellers indicates that tree cover and grasslands were discontinuous and patchy, with many animals living along ecotonal boundaries. Remains of horse, bison, camel, tapir, beaver, dire wolf, and white-tailed deer dating to nearly 18,000 years BP were found in a buried pond deposit on Tilghman Island, Maryland, near the mouth of the Choptank River.40 LGM fossils have been dredged up by various commercial endeavors working the shallow deposits on the continental shelf. Frequently the bones of mammoths, mastodons, whales, and walruses are brought into museums to be identified, whereas less dramatic, smaller specimens are usually not reported (figure 9.3).41

  Submerged locations in northwestern Florida rivers and sinkholes have produced a wealth of extinct faunal remains, primarily mastodon, mammoth, and horse, as well as seal remains.42 In many cases their context indicates that they were killed or scavenged by humans. Carved ivory artifacts found in these deposits have been attributed to Clovis craftspeople, but the radiocarbon dates are somewhat older than Clovis.

  Shawnee Minisink, at the Delaware Water Gap in Pennsylvania, is the only other East Coast Clovis site where perishable remains were preserved. Its association of seeds of edible plants such as hackberry, blackberry, chenopod, hawthorn plum, and grapes indicates a broad range of seasonally edible resources. Unidentified fish remains corroborate this notion and show that fishing technologies were known to Clovis people.

  As with the Solutrean situation, it is difficult to assess the importance of coastal and marine environments for Clovis peoples because these localities are now underwater. However, the great number of Clovis artifacts eroding out on the intertidal zone of the Chesapeake and those dredged up from the bottom of the bay indicate that major occupation sites were located at strategic spots for exploiting the bay and its estuaries.

  A BIRD’S-EYE VIEW OF THE FROZEN NORTH ATLANTIC

  It has been suggested that the LGM North Atlantic waters were too cold and their ecological productivity too low to sustain most animal life, let alone humans.43 Such a blanket assessment reduces the entire North Atlantic and the entire duration of the LGM to a static event, rather than the ever-changing fluid process that it was. Although productivity may have been lower in the seas underlying perennial ice cover, the effects of seasonal freeze-thaw and other natural processes would have enhanced primary biological productivity along the shifting margins of the ice pack.44

  FIGURE 9.4.

  Reconstruction of North Atlantic sea ice cover during the Last Glacial Maximum, with hypothesized Solutrean migration routes. (Based on de Vernal and Hillaire-Marcel 2000; Dyke and Prest 1987; Lambeck 1995; Pflaumann et al. 2003; Preece 1995; Rida and de Vernal 2008.)

  Marine ice exists in many forms, but those most important for this study are perennial ice, seasonal ice, icebergs, and floating ice islands. The paleoceanographers A. de Vernal and C. Hillaire-Marcel used the distributions of dinocysts to define the extent of the LGM sea ice cover.45 Dinocysts do not dissolve as readily as the biogenic carbonates of other fossils; hence, they are relatively abundant and well preserved in the sediments of ocean environments. Some dinocysts are found exclusively in ice-free environments, whereas others predominate in regions with more or less extensive sea ice cover (figure 9.4).46

  As the name implies, the perennial ice pack is always present in the Arctic Ocean, but its extent varies with thermal trends. We are now in a warming stage, and the margins of the pack ice are retreating northward at an alarming rate. During the LGM, when the glacial ice sheets were near their maximum, permanent sea ice formed along the western Atlantic coast as far south as roughly 50° north latitude, or present-day Newfoundland. Sea ice was also periodically distributed around the eastern margin of the North Atlantic, perhaps as far south as the British Isles. Deep-sea cores show that the biological productivity beneath the perennial LGM ice was low, perhaps as much as 50 percent less than today, and life ecozones were shifted southward from their present locations to compensate for these harsher physical conditions. This low productivity nevertheless would have provided enough resources for the Paleolithic people who made their living from the sea.47

  The margins of the perennial sea ice extend when the adjacent water freezes during colder months and shrink by thawing and breakup during warmer months. The ice produced in this manner is called ice of the year or seasonal or annual ice. Seasonal ice can also form on or be blown by storms onto beaches, where it becomes landfast ice. These processes vary, producing annual ice cover that lasts from a year or more to a few weeks or less, depending on short-term weather fluctuations such as a colder than normal year.

  The extent and location of the ice edge is important, because the adjacent surface waters are richer in major nutrients, with algae and plankton particularly abundant.48 The outer margins of the annual ice and landfast ice are relatively fluid, with open-water channels called leads forming and closing. Open leads create microhabitats for various kinds of marine mammals, other sea life, and waterfowl. Polynyas, small ponds of open water formed in the polar oceans and on land-fast ice, provide the habitats relied on by overwintering marine birds and mammals.49

  De Vernal and Hillaire-Marcel suggest that the LGM had large seasonal contrasts in temperature, with very cold winters but relatively warm summers. If the LGM annual ice behaved like its modern equivalent, when temperatures turned warmer it would have begun to melt and crack, forming leads. These channels could close with a change of wind or continue to widen, but eventually the ice would break up into myriad ice islands, both big and small. The islands would float with the current along with the icebergs until they melted in the summer sun. Onshore winds would have driven ice islands onto beaches, where they remained until melted unless freed by tides. Ice islands adjacent to the perennial ice edge would have been reincorporated into the ice mass as temperatures cooled in the fall.

  Annual ice does not form along the coastlines of northwestern Europe today, primarily because the North Atlantic Drift raises the sea surface temperature enough to inhibit its development. During colder episodes of the LGM, however, annual ice formed along the coastline of western Europe. Landfast ice may have been common along the Aquitaine and Cantabrian coasts for several months during winters of the peak cold periods and offshore ice even more common.

  During the coldest periods of the LGM, the polar front, the boundary between the cold waters of the North Atlantic and the warmer waters of the Gulf Stream, is estimated to have been at around 40°N, falling along the coastlines of Portugal and northern New England.50 The Gulf Stream arched eastward from Cape Hatteras and flowed across the Atlantic toward Iceland, then branched southward to skim along the west coast of Europe and northwest coast of Africa before returning to the Caribbean (figure 9.1).51

  Along its northern margin the Gulf Stream clashed with the colder waters of the Labrador Current, bearing icebergs and ice islands on their way south. The icebergs melted faster on mixing with warmer waters, compromising the warmth of the Gulf Stream to a certain degree and releasing tons
of debris; in return, the cold northern waters warmed slightly as they intermingled with the Gulf Stream. In the northeastern ocean the currents turned north again and headed in a large counterclockwise gyre along the coast of northwestern Europe, on to Greenland, and eventually back to Labrador to begin the cycle anew.

  These circumstances produced three parallel zones of surface water types, based on temperature: polar waters, subarctic waters, and warmer Atlantic waters. Their boundaries shifted north or south depending on a variety of climatic and oceanographic phenomena, including short and longer-term thermal cycles. Hence the sea surface temperature of a local water, such as a part of the Bay of Biscay, may have stayed relatively static during one person’s lifetime but shifted so rapidly during another period that people were cognizant of the changes.

  Since it is difficult to recognize these important but subtle changes at the scale of analysis afforded by deep-sea cores, average temperature calculations are only suggestive. That said, the average LGM temperatures of offshore Cantabrian waters at 40°N are estimated to have been between 1.5°C in February and 9.5°C in August, with October and November temperatures reaching as high as 7.0°C.52 At 50°N these temperatures would have been on average about 2°C–12°C colder.53 Atlantic cod can tolerate temperatures from 5°C to 20°C and prefer those ranging between 0°C and 11°C.54 The shallowly submerged Flemish Platform east of the Grand Banks is thought to have been a major cod breeding ground during the LGM.55 Thus, even though the LGM Cantabrian waters were colder than they are today, they were still habitable by cod, an important subsistence resource for humans and other marine predators.

  The continental glaciers discharged massive quantities of icebergs into the North Atlantic at least six times during the LGM. Although the cause of these Heinrich events is unclear, they were probably provoked by internal ice sheet failure or rapid expansion in response to global cooling. Whatever their origin, these events were characterized by a rapid cooling of seawater surface temperatures, decrease in ocean salinity, and marked increase in the percentage of the foraminifer Neogloboquadrina pachyderma, which prefers waters colder than 10°C, in deep-sea cores. Rises in sea surface temperatures immediately after peaks in ice-rafted debris appearance are implied by a decrease of N. pachyderma and an increase of other species such as Globigerina bulloides. Would prehistoric seamen have ventured out on the Atlantic during a Heinrich event, or during the subsequent warming phase? Perhaps because we are landlubbers, we suggest that people began to exploit the sea during the warmer phases, but they might not have waited that long.

  During Heinrich events huge amounts of ice eventually ended up on the southern edge of the polar gyre (figure 9.1). At that latitude, warmer waters from the south accelerated the melting of the ice, leading to a rapid deposition of carbonate-rich IRD in a wide belt across the ocean.56

  The influence of icebergs on phytoplankton production in surface waters is controversial. Some authors suggest that the high diversity and relatively low numbers of benthic foraminifers indicate a low flux of food. Thus, productivity would have decreased during IRD events.57 Others view the lower abundance of these fossils as a preservation artifact and suggest that nutrients released from the melting icebergs created a special environment in the surface waters that was highly productive.58

  Atmospheric and ocean circulation strengthened during the full glacial period. This led to an intensification of upwelling and consequent increase in biological productivity. The diatom and organic carbon content of the LGM section of a core taken off the coast of Portugal indicates that the summer northerly trade winds created such an upwelling of nutrient-enriched waters there.59 Further, the mixing of the Gulf Stream’s warmer waters and the nutrient-rich cold waters would have encouraged the growth of phytoplankton, which in turn would have sustained shoals of fish, sea mammals, and waterfowl.

  The prevailing Canary current would have carried nutrient-enriched waters directly into the Bay of Biscay and intersected with the southern margin of the annual ice. Hence it is highly likely that ice edge–adapted animals would have been common along the ice age coastline of northern Spain and northward. In fact, during various phases of the LGM this region was probably an excellent location for rookeries used by seals and perhaps walruses. Today seals and other marine animals overwinter on pack ice and follow the receding ice into the Arctic waters of the North Atlantic in the summer. These creatures’ ancestors no doubt behaved similarly throughout the LGM and the waning years of the Late Pleistocene, overwintering near the northern Spanish coast and providing ample time for astute and inventive hunters to learn to harvest their rich bounty. These beasts were not only obvious and important sources of the meat, blubber, and blood necessary for withstanding extreme cold environments but also excellent sources of hides, sinew, and gut, the last extremely important for making waterproof clothing. Seals are also an excellent source of oil, which would have been an extremely important resource in the wood-impoverished environment of LGM Spain.

  Common and king eiders and other avian species that overwinter on ice edges, leads, and ponds are important sources of food and down for the Inuit today and would have been available as winter resources for Solutrean hunters. The great auk and other members of its family, as depicted by Solutrean artists in Cosquer Cave, would have been common inhabitants of northwestern European waters.60 These now extinct birds were about the size of a goose and unable to fly. Prized for their feathers, oil, and meat, they were easy prey and could be simply grabbed by hand. Like the other beasts of subarctic waters, the great auk migrated with the ice edge, northward from the Bay of Biscay in the spring and southward in the fall. This behavior pattern is likely to have been ancient, and pre-maritime hunters probably grieved when the last great auk swam away each spring.61

  Much progress has been made in assessing the paleobiodiversity of the earth’s oceans, but the exact processes and interactions involved in creating that diversity are still under debate. It is axiomatic, however, that although the diversity of life-forms decreases from low to high latitudes, the population density of those that survive increases, even in the coldest polar waters. Deep-sea cores show that the density of foraminifera under perennial ice was low, but they were present and, considering sample size and preservation problems, are probably grossly underrepresented. Thus, no matter what the productivity of the LGM North Atlantic ice edge was, the ancestors of the species now present, even if in greatly reduced numbers, would have been sufficient to sustain the impact of predation by Paleolithic hunters.

  The assumption that the LGM ocean was too cold to support life is an oversimplification of the complex paleo-oceanographic processes that took place then. It is our contention that during certain times and at certain latitudes, the LGM North Atlantic not only was capable of sustaining higher forms of life but was a comparatively rich environment that was used, explored, and understood by peoples whose ancestors had faced the ocean for centuries.

  10

  LIVING ON THE ICE EDGE

  Ethnographic Analogies

  It is a reasonable assumption that Atlantic sailors throughout the ages have well understood the regularity of tidal flows and the direction of the prevailing winds, and would have been able to judge the weather patterns with tolerable accuracy before embarking upon a journey.

  BARRY CUNLIFFE, FACING THE OCEAN: THE ATLANTIC AND ITS PEOPLES

  For most modern people life on the edge of the sea ice is as alien as life on Mars, and ignorance of this frozen world prompts many misconceptions and fears. After we make presentations on this topic we are asked the same questions: Wasn’t it dangerous? How could people survive on the ice, especially primitive cavemen? How could they keep warm? What did they use for fuel? What would have been available for food, and how did they find water? Since there is no way to know how Paleolithic people adapted to this environment, we address these and other questions by illustrating key techniques used by the Inuit people of the American Arctic for hunting and surviving on the i
ce edge. Although the Inuit ancestors no doubt took a long time to perfect their adaptations, these techniques evolved from common sense and an acute knowledge of their environment. Here we invoke a convergence of lifeway strategies, as Inuit and Paleolithic peoples faced similar environmental issues, and we base much of the following narrative on the ways that the former have exploited the ice edge.1

  To understand Solutrean lifeways we must consider reconstructions of ice age environments and model the entire ecosystem rather than just the uplands that are currently above sea level. Even though we do not have complete evidence of the ancient natural conditions, we can make assumptions based on our knowledge of the dynamics of sub-arctic marine and coastal environments, especially as to animal behavior and the seasonal influences of winds, currents, and tides. With this ecological information and comparisons to historic and more recent human adaptations to analogous environments, we can better understand this unknown portion of ice age human life.

  Ignoring the fact that the Last Glacial Maximum continental shelves and coastal and oceanic resources were available for people to exploit simply because these areas now rest beneath the sea is a major mistake in reconstructing Solutrean, and possibly pre-Clovis, life. The simple proclamation that the marine environment was too harsh for Paleolithic people to exploit only compounds the error. During the thousands of years that the Solutrean people of northern Spain eked out a living from the narrow strip of land wedged between the ice age sea and ice- and snow-covered mountains, they no doubt observed and learned the many moods of their natural world. The resources of the sea and continental shelf likewise would not have escaped their attention. These early innovators would have tested and pushed their understanding of the ice edge and the sea until they could best take advantage of these environments.