Beyond Refugia: New insights on Quaternary climate variation and the evolution of biotic diversity in tropical South America

Haffer’s (Science 165: 131–137, 1969) Pleistocene refuge theory has provided motivation for 50 years of investigation into the connections between climate, biome dynamics, and neotropical speciation, although aspects of the orig- inal theory are not supported by subsequent studies. Recent advances in paleocli- matology suggest the need for reevaluating the role of Quaternary climate on evolutionary history in tropical South America. In addition to the many repeated large-amplitude climate changes associated with Pleistocene glacial-interglacial stages (~40 kyr and 100 kyr cyclicity), we highlight two aspects of Quaternary climate change in tropical South America: (1) an east-west precipitation dipole, induced by solar radiation changes associated with Earth’s precessional variations (~20 kyr cyclicity); and (2) periods of anomalously high precipitation that persisted for centuries-to-millennia (return frequencies ~1500 years) congruent with cold “Heinrich events” and cold Dansgaard-Oeschger “stadials” of the North Atlantic region. The spatial footprint of precipitation increase due to this North Atlantic forcing extended across almost all of tropical South America south of the equator. Combined, these three climate modes present a picture of climate change with different spatial and temporal patterns than envisioned in the original Pleistocene refuge theory. Responding to these climate changes, biomes expanded and contracted and became respectively connected and disjunct. Biome change undoubtedly influenced biotic diversification, but the nature of diversification likely was more complex than envisioned by the original Pleistocene refuge theory. In the lowlands, intermittent forest expansion and contraction led to species dispersal and subsequent isolation, promoting lineage diversification. These pulses of climate-driven biotic interchange profoundly altered the composition of regional species pools and triggered new evolutionary radiations. In the special case of the tropical Andean forests adjacent to the Amazon lowlands, new phylogenetic data provide abundant evidence for rapid biotic diversification during the Pleistocene. During warm interglacials and intersta- dials, lowland taxa dispersed upslope. Isolation in these disjunct climate refugia led to extinction for some taxa and speciation for others.Peer Reviewedhttps://deepblue.lib.umich.edu/bitstream/2027.42/155561/1/Baker2020.pdfDescription of Baker2020.pdf : Main articl

Rapid climate changes in the tropical Atlantic region during the last deglaciation

The climate system is capable of changing abruptly from one stable mode to another(1-3). Rapid climate oscillations--in particular the Younger Dryas cold period during the last deglaciation--have long been recognized from records throughout the North Atlantic region(4-14), and the distribution of these records at mostly high latitudes suggests that the changes were caused by rapid reorganizations of the North Atlantic thermohaline circulation(6,8,10,15). But events far from the North Atlantic region that are synchronous with the Younger Dryas(16-19) raise the possibility that a more global forcing mechanism was responsible(20). Here we present high-resolution records of laminated sediments of the last deglaciation from the Cariaco basin (tropical Atlantic Ocean) which show many abrupt sub-decade to century-scale oscillations in surface-ocean biological productivity that are synchronous with climate changes at high latitudes. We attribute these productivity variations to changes in or duration of upwelling rate (and hence nutrient supply) caused by changes in trade-wind strength, which is in turn influenced by the thermohaline circulation through its effect on sea surface tempersture(6,21). Abrupt climate changes in the tropical Atlantic during the last deglaciation are thus consistent with a North Atlantic circulation forcing mechanism