Reconstruction Of Climate History Research Articles

Potential Trees Species of North-East India for Dendroclimatological Studies

Many tropical trees show distinct annual ring formation as in temperate conifers, and the growth of these annual rings is used as bio-indicators of environmental changes. Dendroclimatology is the science dealing with the reconstruction of a history of past climate through dendrochronological (tree ring) analysis and assessing the effect of climatic change on tree growth. Trees are living natural archives and their growth is largely impacted by various climatic and non-climatic events occurring in the surrounding environments. In Northeast India, several conifers and broad-leaf tree species such as Abies densa, Larix griffithii, Pinus merkusii, Pinus kesiya, Pinus wallichiana, Quercus serrata, Toona ciliata and Tectona grandis have been used for tree ring-based studies. Dendrochronological studies mainly focused on the reconstruction of climate history, climate-tree growth relationship, river flow history reconstruction, inter-annual density fluctuation, and for development of climate proxies. Among these, the oldest tree ring chronology of Abies densa of 490 years (1504 to 1994) was reported from Yumthang of Sikkim. Whereas the youngest chronology of Toona ciliata of 35 years (1984 to 2018) was from Chandel district of Manipur. The knowledge derived from the detailed study of these species will help forest managers and conservationists to manage the forest in a changing environment. This paper presented dendrochronological information of different trees of northeast India based on the published literature and their possible impact on climate reconstruction through dendroclimatology. However, further potential tree species forming tree rings need to be worked out for possible climate mitigation measures of tropical trees in northeast India.

TRADITIONAL AND EMERGING GEOCHEMICAL PROXIES IN FORAMINIFERA

Geochemical analyses of the carbonate tests calcified by foraminifera have provided much of the foundation for reconstructions of past ocean and climate conditions, and for chemostratigraphy. In particular, reconstructions of climate history (including temperature, salinity, and ice volume), ocean paleocirculation patterns, the carbon cycle, paleoproductivity, marine carbonate chemistry, and chemostratigraphy have relied on measurements of isotopic and trace element composition of foraminiferal calcium carbonate, and variations in these geochemical records through time and space. Substantial work has been done on details of traditional proxies (e.g., d 18 O, d 13 C) and on emerging proxies (e.g., d 11 B, eNd) in recent years; hence, a new overview of these proxies provides a timely reference and educational tool. We review the geochemical proxies that utilize foraminiferal carbonate tests, including potential uses of the proxies for reconstructions through time: d 18 O, d 13 C, trace elements (Mg, Cd, Ba, Zn, B, U), 87 Sr/ 86 Sr, d 26 Mg, d 11 B, and eNd. Both planktic and benthic foraminifera are included; planktic foraminifera provide information on the upper few hundred meters of the surface ocean, whereas benthic foraminifera provide information on conditions at the seafloor and in shallow porewaters, from shallow seas to deep ocean basins.

Solar modulation of Little Ice Age climate in the tropical Andes

The underlying causes of late-Holocene climate variability in the tropics are incompletely understood. Here we report a 1,500-year reconstruction of climate history and glaciation in the Venezuelan Andes using lake sediments. Four glacial advances occurred between anno Domini (A.D.) 1250 and 1810, coincident with solar-activity minima. Temperature declines of -3.2 +/- 1.4 degrees C and precipitation increases of approximately 20% are required to produce the observed glacial responses. These results highlight the sensitivity of high-altitude tropical regions to relatively small changes in radiative forcing, implying even greater probable responses to future anthropogenic forcing.