Millennial-scale vegetation changes in the tropical Andes using ecological grouping and ordination methods

We compare eight pollen records reflecting climatic and environmental change from northern and southern sites in the tropical Andes. Our analysis focuses on the last 30ĝ€ 000 years, with particular emphasis on the Pleistocene to Holocene transition. We explore ecological grouping and downcore ordination results as two approaches for extracting environmental variability from pollen records. We also use the records of aquatic and shoreline vegetation as markers for lake level fluctuations and moisture availability. Our analysis focuses on the signature of millennial-scale climate variability in the tropical Andes, in particular Heinrich stadials (HS) and Greenland interstadials (GI). The pollen records show an overall warming trend during the Pleistocene-Holocene transition, but the onset of post-glacial warming differs in timing among records. We identify rapid responses of the tropical vegetation to millennial-scale climate variability. The signatures of HS and the Younger Dryas are generally recorded as downslope upper forest line (UFL) migrations in our transect, and are likely linked to air temperature cooling. The GI1 signal is overall comparable between northern and southern records and indicates upslope UFL migrations and warming in the tropical Andes. Our marker for lake level changes indicated a north-To-south difference that could be related to moisture availability. The air temperature signature recorded by the Andean vegetation was consistent with millennial-scale cryosphere and sea surface temperature changes but suggests a potential difference between the magnitude of temperature change in the ocean and the atmosphere. We also show that arboreal pollen percentage (AP %) and detrended correspondence analysis (DCA) scores are two complementary approaches to extract environmental variability from pollen records

Parallelisms between sea surface temperature changes in the western tropical Atlantic (Guiana Basin) and high latitude climate signals over the last 140 000 years

Sea surface temperatures (SST) in the Guiana Basin over the last 140 ka were obtained by measuring the C37 alkenone unsaturation index Uk'37 in the sediment core MD03-2616 (7° N, 53° W). The resulting data set is unique in the western tropical Atlantic region for this period. The SSTs range from 25.1 to 28.9 °C, i.e. glacial-interglacial amplitude of 3.8 °C, which is in the range of change of other tropical areas. During the last two interglacial stages (marine isotope stages; MIS1 and MIS5e) and warm long interstadials (MIS5d-a), a rapid transmission of climate variability from Arctic-tropical latitudes is recorded. During these periods, the MD03-2616 SSTs show a conspicuous parallelism with temperature changes observed in Greenland and SST records of North Atlantic mid-latitude cores (Iberian Margin 38° N, Martrat et al., 2007). The last deglaciation in the Guiana Basin is particularly revealing. MIS2 stands out as the coldest period of the interval analysed. The events recorded in Guiana parallel northern latitude events such as the Bølling-Allerød warming and the Younger Dryas cooling which ensued. These oscillations were previously documented in the δ18O of the Sajama tropical ice core (Bolivia) and are present in Guiana, with rates of ca. 6 °C ka-1 and changes of over 2 °C. During the glacial interval, significant abrupt variability is observed, e.g. oscillations of 0.5-1.2 °C during MIS3, which is about 30 % of the maximum glacial-interglacial SST change. In the MD03-2616 record, it is possible to unambiguously identify either the Dansgaard-Oeschger oscillations described in northern latitudes or the SST drops associated with the Heinrich events characteristic of North Atlantic records. Although these events form the background of the climate variability observed, what truly shapes SSTs in the Guiana Basin is a long-term tropical response to precessional changes, which is modulated in the opposite way to Northern Hemisphere variability. This lack of synchrony is consistent with other tropical records in locations to the north or south of the Guiana Basin and evidences an Arctic-tropical decoupling when a substantial reduction in the Atlantic meridional overturning circulation (AMOC) takes place. © Author(s) 2015. CC Attribution 3.0 License.Peer reviewe

The global abundance of tree palms

Aim Palms are an iconic, diverse and often abundant component of tropical ecosystems that provide many ecosystem services. Being monocots, tree palms are evolutionarily, morphologically and physiologically distinct from other trees, and these differences have important consequences for ecosystem services (e.g., carbon sequestration and storage) and in terms of responses to climate change. We quantified global patterns of tree palm relative abundance to help improve understanding of tropical forests and reduce uncertainty about these ecosystems under climate change. Location Tropical and subtropical moist forests. Time period Current. Major taxa studied Palms (Arecaceae). Methods We assembled a pantropical dataset of 2,548 forest plots (covering 1,191 ha) and quantified tree palm (i.e., ≥10 cm diameter at breast height) abundance relative to co‐occurring non‐palm trees. We compared the relative abundance of tree palms across biogeographical realms and tested for associations with palaeoclimate stability, current climate, edaphic conditions and metrics of forest structure. Results On average, the relative abundance of tree palms was more than five times larger between Neotropical locations and other biogeographical realms. Tree palms were absent in most locations outside the Neotropics but present in >80% of Neotropical locations. The relative abundance of tree palms was more strongly associated with local conditions (e.g., higher mean annual precipitation, lower soil fertility, shallower water table and lower plot mean wood density) than metrics of long‐term climate stability. Life‐form diversity also influenced the patterns; palm assemblages outside the Neotropics comprise many non‐tree (e.g., climbing) palms. Finally, we show that tree palms can influence estimates of above‐ground biomass, but the magnitude and direction of the effect require additional work. Conclusions Tree palms are not only quintessentially tropical, but they are also overwhelmingly Neotropical. Future work to understand the contributions of tree palms to biomass estimates and carbon cycling will be particularly crucial in Neotropical forests

Regional vegetation changes in the tropical Andes expressed as arboreal pollen (AP%), standardised ordination scores (DCA z-scores), and aquatic vegetation ratios (D/SS); files used for plots

We compare eight pollen records reflecting climatic and environmental change from the tropical Andes. Our analysis focuses on the last 50 ka, with particular emphasis on the Pleistocene to Holocene transition. We explore ecological grouping and downcore ordination results as two approaches for extracting environmental variability from pollen records. We also use the records of aquatic and shoreline vegetation as markers for lake level fluctuations, and precipitation change. Our analysis focuses on the signature of millennial-scale variability in the tropical Andes, in particular, Heinrich stadials and Greenland interstadials. We identify rapid responses of the tropical vegetation to this climate variability, and relate differences between sites to moisture sources and site sensitivity

Rapid millennial-scale vegetation changes in the tropical Andes

We compare eight pollen records reflecting climatic and environmental change from the tropical Andes. Our analysis focuses on the last 50 ka, with particular emphasis on the Pleistocene to Holocene transition. We explore ecological grouping and downcore ordination results as two approaches for extracting environmental variability from pollen records. We also use the records of aquatic and shoreline vegetation as markers for lake level fluctuations, and precipitation change. Our analysis focuses on the signature of millennial-scale variability in the tropical Andes, in particular, Heinrich stadials and Greenland interstadials. We identify rapid responses of the tropical vegetation to this climate variability, and relate differences between sites to moisture sources and site sensitivity

Parallelisms between sea surface temperature changes in the western tropical Atlantic (Guiana Basin) and high latitude climate signals over the last 140 000 years

Sea surface temperatures (SST) in the Guiana Basin over the last 140 ka were obtained by measuring the C37 alkenone unsaturation index Uk'37 in the sediment core MD03-2616 (7° N, 53° W). The resulting data set is unique in the western tropical Atlantic region for this period. The SSTs range from 25.1 to 28.9 °C, i.e. glacial–interglacial amplitude of 3.8 °C, which is in the range of change of other tropical areas. During the last two interglacial stages (marine isotope stages; MIS1 and MIS5e) and warm long interstadials (MIS5d-a), a rapid transmission of climate variability from Arctic–tropical latitudes is recorded. During these periods, the MD03-2616 SSTs show a conspicuous parallelism with temperature changes observed in Greenland and SST records of North Atlantic mid-latitude cores (Iberian Margin 38° N, Martrat et al., 2007). The last deglaciation in the Guiana Basin is particularly revealing. MIS2 stands out as the coldest period of the interval analysed. The events recorded in Guiana parallel northern latitude events such as the Bølling–Allerød warming and the Younger Dryas cooling which ensued. These oscillations were previously documented in the δ18O of the Sajama tropical ice core (Bolivia) and are present in Guiana, with rates of ca. 6 °C ka−1 and changes of over 2 °C. During the glacial interval, significant abrupt variability is observed, e.g. oscillations of 0.5–1.2 °C during MIS3, which is about 30 % of the maximum glacial–interglacial SST change. In the MD03-2616 record, it is possible to unambiguously identify either the Dansgaard–Oeschger oscillations described in northern latitudes or the SST drops associated with the Heinrich events characteristic of North Atlantic records. Although these events form the background of the climate variability observed, what truly shapes SSTs in the Guiana Basin is a long-term tropical response to precessional changes, which is modulated in the opposite way to Northern Hemisphere variability. This lack of synchrony is consistent with other tropical records in locations to the north or south of the Guiana Basin and evidences an Arctic–tropical decoupling when a substantial reduction in the Atlantic meridional overturning circulation (AMOC) takes place

Millennial-scale vegetation changes in the tropical Andes using ecological grouping and ordination methods

We compare eight pollen records reflecting climatic and environmental change from northern and southern sites in the tropical Andes. Our analysis focuses on the last 30 000 years, with particular emphasis on the Pleistocene to Holocene transition. We explore ecological grouping and downcore ordination results as two approaches for extracting environmental variability from pollen records. We also use the records of aquatic and shoreline vegetation as markers for lake level fluctuations and moisture availability. Our analysis focuses on the signature of millennial-scale climate variability in the tropical Andes, in particular Heinrich stadials (HS) and Greenland interstadials (GI). The pollen records show an overall warming trend during the Pleistocene-Holocene transition, but the onset of post-glacial warming differs in timing among records. We identify rapid responses of the tropical vegetation to millennial-scale climate variability. The signatures of HS and the Younger Dryas are generally recorded as downslope upper forest line (UFL) migrations in our transect, and are likely linked to air temperature cooling. The GI1 signal is overall comparable between northern and southern records and indicates upslope UFL migrations and warming in the tropical Andes. Our marker for lake level changes indicated a north-to-south difference that could be related to moisture availability. The air temperature signature recorded by the Andean vegetation was consistent with millennial-scale cryosphere and sea surface temperature changes but suggests a potential difference between the magnitude of temperature change in the ocean and the atmosphere. We also show that arboreal pollen percentage (AP %) and detrended correspondence analysis (DCA) scores are two complementary approaches to extract environmental variability from pollen records