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A palaeoclimate and palaeoecological study was carried out using
sedimentological, palynological and thecamoebian evidence in a 5 m deep
sediment core deposited since ~3630 cal BP from TSpettai mangrove wetland,
northeastern part of Cauvery River Delta. Textural analysis shows the
overall predominance of fine clay with intermittent phases of sand. The
palynological climatic period inferred in Phase I (~3630-3170 cal BP) shows
a stabilized estuarine ecosystem conducive for mangroves along with a good
percentage of hinterland forest indicating a warm and humid climate with
strengthened monsoon. Phase IIa (~3170-2600 cal BP) shows abundance of
salt-tolerant mangroves along with a mixed forest suggesting climatic
amelioration from warm and humid to dry and arid. Phase IIb (~2600-1300 cal
BP) shows the dominance of salt tolerant species indicating enhanced dry
and arid climate coupled with weakened monsoon. Phase III (since ~1300 cal
BP) is characterized by rejuvenation of true mangroves and high percentages
of salinity tolerant mangroves with a low percentage of thecamoebians,
thereby indicating increased salinity induced by weakened monsoon and
enhanced anthropogenic activity. It is inferred that during the past 3
millennia, climate changed from warm and humid to cool and arid conditions,
with an evolution of vegetation from moist to dry deciduous forest. The
qualitative and quantitative study shows a decline in the true mangroves
and an increase in the salt tolerant vegetation, which is attributed to the
increased salinity in the wetland due to high salt accumulation in the root
zone which is vulnerable for mangroves.
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