Mangrove vegetation responses to Holocene climate change along Konkan coast of south-western India

摘要

The pollen signatures preserved in the mangrove sediments provided records of species variation over a period of time with past climate and sea level changes. The Airoli profile has a Late Pleistocene sequence, and all the other studied profiles and intervals cover the Holocene only. The absence of mangrove signatures during the Late Pleistocene interval is attributed to a relatively low sea level. The ideal conditions for mangrove development along Konkan prevailed during Middle Holocene, when the first extensive mangrove swamps appeared in Sindhudurg (Dhamapur-Hadi) area particularly between 7220 and 4770 yrs BP. This period coincides with the Holocene Climate Optimum (HCO) when Monsoon Asia witnessed much higher precipitation. However, the mangroves responded to environmental changes due to relative abundance of fresh water leading to change in species composition. Two different scenarios of mangrove response during the Late Holocene, one in Dhamapur and the other in Palm Beach, are found to be significant. The Rhizophora-Sonneratia transition from Early Mid-Holocene to Late Holocene is considered to be the most distinctive feature. The decline of mangroves since 3500 yrs BP and further degradation has been attributed to the prevailing arid climate and weakening trends of the monsoon until 1500 yrs BP. However, there seems to be a positive trend in emergence of mangroves in the least disturbed areas of south Konkan, attributed to strengthening of summer monsoon in the recent past.