 |
| Titel |
Past Temperature and Salinity of the Eastern Arabian Sea: Implications to
Sun-Monsoon Precipitation Relationship over Past Couple of Millennia |
| VerfasserIn |
Manish Tiwari, Siddhesh Nagoji, Raja Ganeshram |
| Konferenz |
EGU General Assembly 2016
|
| Medientyp |
Artikel
|
| Sprache |
Englisch
|
| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 18 (2016) |
| Datensatznummer |
250121531
|
| Publikation (Nr.) |
 EGU/EGU2016-294.pdf |
|
|
|
|
|
| Zusammenfassung |
| Eastern Arabian Sea is one of the few regions from where not many high-resolution records
of sea surface temperature (SST) and salinity exist despite its hydrological importance
vis-à-vis South Asian summer monsoon precipitation. During this period, significant changes
in salinity occur in the eastern Arabian Sea due to orographic precipitation and runoff.
Additionally, minimal bioturbation occurs in coastal sediments accumulating rapidly due to
the presence of an oxygen minima zone (OMZ) in the Arabian Sea. The sediment core used
in this study was collected offshore Mangalore from the middle of the OMZ from a
water depth of 589 m. The core spans a period of 154 to 4772 yr BP. The average
sedimentation rate is 8.96 cm/Kyr while the average resolution is ∼112 yrs/cm. The
stable oxygen isotope content (δ18Oc) was determined on the planktic foraminifera
Globigerinoides ruber while the past SST variations were determined using an independent
parameter - Mg/Ca - in the same species. The salinity was obtained by delineating SST
from the δ18Oc using empirical equations. The salinity varies from a maximum of
35.5 (arid) to a minimum of 32.4 (wet) while the SST varies from varies from a
maximum of 29.9˚ C to a minimum of 27.5˚ C - a variability of 2.4˚ C. Such high
variability could be during to its coastal location, which is affected by moderate
upwelling during monsoon season. The long-term trend determined through linear
regression shows that the salinity has been increasing since mid-Holocene implying
increasing aridity. We identify periods of aridity during the Little Ice Age (and a
few centuries prior to it) and at 1300 yr BP, 2000 yr BP, and 4600 yr BP. A few
paleomonsoon records also exhibit prominent correspondence with solar activity
during early Holocene and beyond. But despite the strong recent solar minima (e.g.
Maunder, Spörer, Oort, Wolf), their correlation with monsoon precipitation is weak and
inconclusive. Additionally, those from the western Arabian Sea provide records of
monsoon wind intensity and not the monsoon precipitation. We show that the monsoon
precipitation declined in phase with the solar activity during the recent periods of major
solar minima. Interestingly, this relationship changes beyond 1300 yr BP where
precipitation lagged the solar activity by a couple of hundred years. This is confirmed
through spectral analysis (Continuous Wavelet Transform and the Squared Wavelet
Coherence) and also through comparison with earlier marine and terrestrial studies. |
|
|
|
|
|
|