Despite the universal chorus of politicized alarmists, earth is currently experiencing a period of relative climatic stability compared to the dramatic climatic fluctuations that occurred during the Pleistocene. The presence of vast ice sheets in the northern hemisphere contributed to this ancient climatic instability. Glaciers blocked rivers, creating huge glacial lakes. Warm spikes in average annual temperatures weakened the ice dams and caused breaches. Massive outflows of frigid fresh water and icebergs periodically flooded into the North Atlantic, shutting down thermohaline circulation. The gulf stream normally carries tropically heated water into the North Atlantic, and this keeps overall climate temperate, but after torrents of cold fresh water stopped this process, average annual temperatures dropped as much as 15 degrees F in less than a decade, precipitating severe stadial conditions that lasted for hundreds or even thousands of years. These meltwater pulses are known as Heinrich events, named after the scientist who first recognized this cycle.
During Ice Ages warm stages of climate cyclically caused glacier dams to burst, releasing massive amounts of cold fresh water plus icebergs. This shut down the North Atlantic Gulf Stream which brings tropically heated water north, resulting in a sudden decline in average annual temperatures.
A graph showing average annual temperature fluctuations over the last 100,000 years from data gleaned inside Greenland ice cores. Cyclical Heinrich Events caused the sudden declines in temperatures.
I assumed Heinrich Events severely disrupted marine ecosystems, causing decisive population declines in most fish and other ocean fauna, though a few species may have benefitted from reduced competition or other factors. But I thought there would be no paleontological evidence because preservation and detection of animal remains during brief time intervals in marine environments seemed unlikely. However, a recent paper highlights evidence that Heinrich Events were detrimental to marine life. Scientists found this evidence in a seaside Sicilian cave named la Grotta Dell’Uzzo. This cave had previously revealed the Pleistocene remains of mammoth, rhino, lion, red deer, and wild boar. Humans have also periodically occupied this cave from the late Pleistocene through the Holocene, and scientists have excavated human skeletons, artifacts, and food remains. Chemical analysis of human bones found in the cave helped scientists determine the diet of the hunter-gatherers who occupied the cave during the early Holocene. They ate red deer, wild boar, shellfish, fish caught near shore (such as grouper), acorns, grapes, and wild beans and peas. However, 1 human specimen and 1 red fox bone, dating to 8200 BP, revealed an interesting difference. Both the human and the fox ate unusual quantities of whale meat during their lifetimes. Red foxes don’t normally include whale meat in their diet, and humans from other generations of cave dwellers here hardly ever exploited this resource. Moreover, whale bones with butcher marks on them were found associated with the human and fox specimens in the same strata. The scientists who examined this evidence determined humans exploited climate-driven whale strandings at this locality.
Mass stranding of pilot whales in Australia. Heinrich Events disrupted marine ecology and caused high annual mortality among many species of whales.
Evidence of early Holocene mass whale strandings was discovered in this seaside cave in Sicily, known as la grotto dell’Uzzo.
The last major Heinrich Event occurred 8200 years ago, following the final dissolution of glacial Lake Agassiz in Canada. This massive meltwater pulse disrupted fish migrations and reduced fish populations, making it harder for many species of whales to find prey. Stressed and malnourished whales are more likely to strand on beaches. The Gulf of Castallammare, adjacent to la Grotto Dell’Uzzo, is an acoustic dead zone difficult for whales to navigate. This is where frequent, probably annual, whale strandings occurred for centuries, and the evidence suggests humans and foxes exploited this resource. Based on the zooarchaeological record, the most common species of whales stranded here were pilot whales (Globicephala melus), Risso’s dolphin ( Grampus griseus ), and short-beaked common dolphin ( Delphinus dolphio ). Frequent whale strandings likely occurred worldwide following Heinrich Events. Off the coast of North America dire wolves, bears, and other large carnivores scavenged this wealth of protein during the Pleistocene. There were certain spots, such as the 1 in Sicily, where carnivores learned to regularly search for this bounty. Carnivore populations may have been higher near the coast due to this additional resource. Unfortunately, evidence of these sites were long ago inundated by rising sea level.
Marcello, Mannino; at. al.
“Climate-driven Environmental Changes around 8200 Years Ago Favored Incidences of Cetacean Strandings and Mediterranean Hunter-Gatherers Exploited Them”
Scientific Reports 2015