Understanding past abrupt climate instabilities in the North Atlantic Region (ULTImATum)

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Pollen from the deep-sea: A breakthrough in the mystery of the ice ages

Publication . Goni, Maria F. Sanchez; Desprat, Stephanie; Fletcher, William J.; Morales-Molino, Cesar; Naughton, Filipa; Oliveira, Dulce; Urrego, Dunia H.; Zorzi, Coralie

Pollen from deep-sea sedimentary sequences provides an integrated regional reconstruction of vegetation and climate (temperature, precipitation, and seasonality) on the adjacent continent. More importantly, the direct correlation of pollen, marine and ice indicators allows comparison of the atmospheric climatic changes that have affected the continent with the response of the Earth's other reservoirs, i.e., the oceans and cryosphere, without any chronological uncertainty. The study of long continuous pollen records from the European margin has revealed a changing and complex interplay between European climate, North Atlantic sea surface temperatures (SSTs), ice growth and decay, and high-and low-latitude forcing at orbital and millennial timescales. These records have shown that the amplitude of the last five terrestrial interglacials was similar above 40 degrees N, while below 40 degrees N their magnitude differed due to precession-modulated changes in seasonality and, particularly, winter precipitation. These records also showed that vegetation response was in dynamic equilibrium with rapid climate changes such as the Dangaard-Oeschger (D-O) cycles and Heinrich events, similar in magnitude and velocity to the ongoing global warming. However, the magnitude of the millennial-scale warming events of the last glacial period was regionally-specific. Precession seems to have imprinted regions below 40 degrees N while obliquity, which controls average annual temperature, probably mediated the impact of D-O warming events above 40 degrees N. A decoupling between high-and low-latitude climate was also observed within last glacial warm (Greenland interstadials) and cold phases (Greenland stadials). The synchronous response of western European vegetation/climate and eastern North Atlantic SSTs to D-O cycles was not a pervasive feature throughout the Quaternary. During periods of ice growth such as MIS 5a/4, MIS 11c/b and MIS 19c/b, repeated millennial-scale cold-air/warm-sea decoupling events occurred on the European margin superimposed to a long-term air-sea decoupling trend. Strong air-sea thermal contrasts promoted the production of water vapor that was then transported northward by the westerlies and fed ice sheets. This interaction between long-term and shorter timescale climatic variability may have amplified insolation decreases and thus explain the Ice Ages. This hypothesis should be tested by the integration of stochastic processes in Earth models of intermediate complexity.

2018Journal article

Open access

Understanding the Atlantic influence on climate and vegetation dynamics in western Iberia over the last 2000 years

Publication . Santos, Ricardo N.; Rodrigues, Teresa; Naughton, Filipa; Schefuß, Enno; Oliveira, Dulce; Moreno, João; Raposeiro, Pedro M.; Gil-Romera, Graciela; Morgan, Alistair; Leira, Manel; Gomes, Sandra D.; Ladd, S. Nemiah; Trigo, Ricardo M.; Ramos, Alexandre M.; Hernández, Armand

Predicting the environmental impact of climate change in extremely sensitive areas, like western Iberia, requires an understanding of the long-term interactions between climate and vegetation. Here we present a novel hightemporal resolution multiproxy analysis, including plant-wax n-alkane isotope data, pollen analysis, macrocharcoal identification, chironomid and diatom records of sediments from a mountain lake in central Portugal. We examined the evolution of the Atlantic and Mediterranean climate influences over the last two millennia, exploring their connection with major atmospheric patterns and impacts on the climatic signal and vegetation dynamics in this understudied region. During the Roman Period (RP; ca. -200 – 500 AD), the study area was characterized by grass dominance, with high temperatures indicated by chironomid composition and microcharcoal content. The increase in plant-wax δ2 H values during this period suggests a shift from wet to dry conditions. The Early Middle Ages (EMA; ca. 500–900 AD) were characterized by colder and a transition to wetter conditions, as indicated by the vegetation and plant-wax n-alkane isotope data. The Medieval Climate Anomaly (MCA; ca. 900–1300 AD) was generally warm, with a short initial lake level drop. This period exhibits the maximum expansion of the Mediterranean forest over the last 2 ka and possibly proximal moisture sources. During the Little Ice Age (LIA; 1300–1850 AD), a reduction of the Mediterranean forest and a strong depletion of plant-wax δ2 H values suggest cold and wet conditions with strong influence of remote Atlantic moisture, with the coldest and wettest phase of the last 2 ka detected between 1550 and 1900 AD. The post-LIA period, from 1900 AD onwards, shows a change to the present warmer and drier conditions, in a highly anthropized landscape. We also demonstrate that major changes in climate have influenced vegetation patterns, with these changes mainly controlled by large-scale atmospheric dynamics. This underscores the sensitivity of western Iberian ecosystems to climate shifts, enriches the current regional understanding of climate-vegetation interplay, and offers valuable insights for future climate change projections.

2024-08Journal article

Open access