Indian monsoon

The history of the Somali upwelling during the last 18.5 ka has been reconstructed using biogenic silica fluxes estimated from a sediment core retrieved from the western Arabian Sea. The reconstructed record demonstrates periodic weakening and strengthening of the Somali upwelling during the past 18.5 ka. Variations in biogenic silica fluxes suggest weak upwelling during the last glacial period (18.5–15 ka BP). Strengthened upwelling during the Bølling–Allerød period (15–13 ka BP) points to post-glacial onset of the southwest monsoon. The Younger Dryas (13–11 ka BP) is again marked by reduced upwelling strength. Intensification of the Somali upwelling at the beginning of the Holocene and a decline at 8 ka BP are observed. Increases in upwelling strength recorded since 8 ka BP suggest strengthening of the southwest monsoon during the latter part of the Holocene. Linking these upwelling variations with southwest monsoon precipitation, a major shift in the relationship between the strength of the Somali upwelling and southwest monsoon rainfall from positive to negative has occurred during the pre-Holocene to the Holocene. The observed shift is attributed to the variation in the southwest monsoon strength due to the latitudinal shift of the Intertropical Convergence Zone (ITCZ) associated with changes in moisture sources.

Planktonic foraminifeml abundances, fluxes, test sizes, and coiling properties are influenced in various ways by the southwest monsoon winds and associated upwelling in the western Arabian Sea. To determine the short-term changes in the southwest monsoon, we have camed out a high-resolution time-series analysis of three upwelling indices (total flux of planktonic foraminiferal tests and flux and relative abundance of the planktonic foraminiferal species Globigerina bulloides) from Ocean Drilling Program (ODP) Site 723A (Oman Margin, western Arabian Sea) spanning the last 19 kyr. In addition, we have determined the relationships between upwelling intensity and the relative abundance, fluxes, and shell concentrations of various planktonic foraminiferal species. Upwelling indices suggest that from 19 to 16 ka (22 to 18.2 cal kyr B.P.) the SW monsoon was relatively strong compared to the period 15.8 to 12.5 ka (17.8 to 13.8 cal kyr B.P.). The intensification of the SW monsoon took place at 12 ka (13.1 cal kyr B.P.) and reached a peak between 10 and 5 ka (10.6 and 4.8 cal kyr B.P.). The high-resolution data further demonstrate that the SW monsoon has started weakening from 5 ka (4.8 cal kyr B.P.) and the weakest phase was in place at 3.5 ka (3 cal kyr B.P.), which coincides with evidence of an arid climate in western Tibet. Fluxes and shell concentrations of many of the planktonic foraminiferal species increased between 12 and 5 ka in response to the intensification of the SW monsoon winds after the last glacial period. Globigerina bulloides shows a fivefold to tenfold increase in flux during this period of intense upwelling. The other species whose fluxes are influenced by this upwelling change are (in order from strongest to weakest response) Globigerinita glutinata, Globigerinoides ruber, Neogloboquadrina dutertrei, Globigerinella aequilateralis, Globigerina falconensis, and Globigerinoides sacculifer. The relative abundances of G. bulloides and G. ruber increased during intense upwelling, whereas the relative abundances of G. glutinata, N. dutertrei, G. falconensis, and G. sacculiJkr did not increase during this period, which might be due to differences in the productivity of various species in relation to upwelling change. Therefore the fluxes and shell concentrations provide better and more reliable information about the changes in the monsoon system in the Arabian Sea than relative abundance data.

ABSTRACT A high resolution record of the Indian summer monsoon (ISM) is generated using a δ18O time series from a stalagmite collected from the Valmiki cave in southern India. This record covers a time span of ~ 1,000 years from 15,700 to 14,700 yr BP (before 1950 AD) with an average sampling resolution of ~ 5 years. High amplitude δ18O variation in this record reflects abrupt changes in ISM activity during the last deglaciation and suggest an age for the onset of Termination 1a (T1a) at ~ 14,800 yr BP in the Indian sub-continent. This record shows evidence for strong changes in tropical climate during the last deglaciation. Coincident variability in VSPM4 δ18O with speleothems from southern China during Termination 1a suggests that these caves reflect fluctuations in ISM activity. The variance in δ18O amplitude reveals significant multidecadal variability in ISM activity. Our record reveals intervals of strong monsoon activity during the later phase of Heinrich event 1 (H1) and shows synchronous multidecadal variability between ISM and East Asian monsoon (EAM). Spectral analysis of δ18O time series in VSPM4 reveals solar forcing and strong ocean-atmospheric circulation control on ISM dynamics during the studied time interval.

Indian summer monsoon has a large inter-annual as
well as intra-seasonal variability over temporal and
spatial scales. Onset dates, monsoon activity within a
monsoon season and quantity of monsoon rainfall are
also found to vary from year to year. One important
synoptic feature associated with the onset of monsoon
is the existence of a strong cross equatorial low level
jet (LLJ), with its core around 850 hPa over the Indian
Ocean and South Asia. This LLJ generally supports
the large-scale moisture and momentum transport
from ocean to atmosphere and the consequent rainfall
over the Indian mainland. In the present study, buoy
data at a stationary position in the Arabian Sea
(15.5°N, 61.5°E) have been used to understand the
air–sea interface processes before, during and after
the onset of monsoon 1995.

Many speleothems exhibit luminescence when exposed to ultraviolet (UV) light sources or other high energy beams. For detailed explanation of luminescence types and properties of minerals reffer to Shopov (1997).
Almost 50 cave minerals have the capacity for exhibiting luminescence, but only 17 had actually observed to be luminescent in speleothems so far.
Most known luminescent centers in calcite are inorganic ions of Mn,Tb, Er, Dy, U, Eu, Sm and Ce. Statements that Sr causes luminescence of carbonates and Cu- causes luminescence of calcite and aragonite are in error. Also interpretations of the visible luminescence of calcite as Pb- activated (Slacik, 1976) are not correct, because Pb in calcite is emitting only UV light.
Minerals contain many admixtures. Usually several centres activate luminescence of the sample and the measured spectrum is a sum of the spectra of two or more of them.
Conventional luminescent research methods have number of disadvantages, so several special speleothem research methods has been developed (table 1)

Luminescence of minerals formed at normal cave temperatures is due mainly to molecular ions and sorbated organic molecules (photo 1). Luminescence of uranil- ion (photo 2) is also very common in such speleothems. Before using a speleothem for any paleoenvironmental work it is necessary to determine that all luminescence of the sample is due to organics.
Calcite speleothems frequently display luminescence which is produced by calcium salts of humic and fulvic acids derived from soils above the cave (Shopov, 1989a,b, White and Brennan, 1989). These acids are released by the roots of living plants, and by the decomposition of dead vegetative matter. Root release is modulated by visible solar radiation via photosynthesis, while rates of decomposition depend exponentially upon soil temperature. The soil temperature depends mainly on solar infrared and visible radiation (Shopov et al., 1994) in case that cave is covered only by grass or upon air temperatures in case that cave is covered by forest or bush. In the first case, microzonality of luminescence of speleothems can be used as an indirect Solar Activity (SA) index (Shopov et al., 1990), but in the second case it can be used as a paleotemperature proxy (Shopov et al., 1996a).
A time series of a Solar Activity (SA) index "Microzonality of Luminescence of Speleothems" can be obtained by Laser Luminescence Microzonal analysis (LLMZA) of cave flowstones (table 1).
Luminescence organics in speleothems can be divided to 4 types:- (1) Calcium salts of Fulvic acids, (2) Calcium salts of humic acids, (3) Calcium salts of huminomelanic acids and (4) Organic esters (Shopov, M. Williams, personal communication). All these four types are usually present in a single speleothem with hundreds of chemical compounds with similar chemical behavior, but of different molecular weights. Concentration distribution of these compounds (and their luminescence spectra) depends on type of soils and plants over the cave, so the study of luminescent spectra of these organic compounds can give information about paleosoils and plants in the past (White, Brennan, 1989). Changes in visible color of luminescence of speleothems suggesting major changes of plants society are observed very rare (photo 3).
Speleothem growth rate may vary significantly within a single speleothem, (Shopov, et al.1992, 1994). This variations represent rainfall variations in case there are no growth interruptions (hiatuses) in studied part of the speleothem (Shopov et al.,1996-c). Luminescence technique visualize annual microbanding (Shopov et al., 1988), not visible in normal light (photo 4). If this banding is visible in normal light or luminescent curves have sharp profiles or jumps like in Baker et al. (1993) it suggests that speleothem growth stoped for a certain period during the year and such time series are not useful for obtaining of rainfall proxy records.
Luminescence of the high temperature hydrothermal minerals is mainly due to cations because molecular ions and molecules destruct at high temperatures. So it indicates the hydrothermal conditions under which the cave minerals forms (photo 5). Minerals deposited by low-temperature hydrothermal solutions have short-life fluorescence due to cations and long phosphorescence due to molecular ions.If calcite has only orange-red, short-life phosphorescence, it is sure to have formed by high-temperature, hydrothermal solutions(>300o C). But if it has also long-time phosphorescence, then it is a low-temperature hydrothermal calcite (Shopov, 1989a,b). Minimal temperatures for the appearance of this orange- red luminescence was estimated between 46o C and 60o C. Luminescence of hydrothermal calcite formed at lower temperatures (photo 6) looks similar to usual speleothem luminescence shown in photo 1.
The tectonic uplift of an area (i.e., uplift of bedrock) can be deduced by luminescence in combination with the absolute dating methods (Shopov et al.,1996-d) if its luminescence is due to epithermal mineralization forming solutions in the older part of the speleothem, but the mixing of these waters with surface waters containing organics appear in younger parts of the speleothem.
Finally, speleothem's luminescence may be used to determine the absolute age of the speleothem itself (Shopov et al., 1991a, Dermendjiev et al.(1996) by Autocalibration dating, which is shown to be the most precise speleothem dating method for samples younger than 2000 years (Shopov et.al, 1994), see entry on Speleothem Dating.

Works cited
Baker,A.,Smart, P.L., Edwards, R.L., and Richards, D.A, 1993, Annual Growth banding in a cave stalagmite: Nature, v.304, p. 518-520.
Dermendjiev V., Shopov Y.Y., Buyukliev G.N.(1996) High- Precision Method of Cave Deposits Dating and an Implication for Archeometric Study.- Physical and Chemical Technics J. 45, IV.7, pp. 307-312.
Gilson, R.J., and Macarthney, E., 1954, Luminescence of speleothems from Devon, U.K.: The presence of organic activators: Ashford Speleological Society Journal, v.6,p.8.
Shopov Y.Y.,Grynberg M.A.,1985.A New Method for Direct Photography of Luminescence.-Exped.Ann.Sofia Univ.,v.1,p.139-45
Shopov Y.Y.,Tsankov L.T.(1985)A Photographic Apparatus for Luminescent Analysis (B. Patent 40439 from 30 Aug. 1985) Bulletin of IIR,v.12,Dec.1986,7 pp.
Shopov Y.Y.,1987, Laser Luminescent MicroZonal Analysis- A New Method for Investigation of the Alterations of the Climate and Solar Activity during Quaternary- in "Problems of Karst Study of Mountainous Countries",MEISNIEREBA,Tbilisi, pp.228-232
Shopov Y.Y.,Dermendjiev V.N.,Buyukliev G.I.,Georgiev L.N, Stoychev T.S. (1988) Investigations on the Variations of the Solar Activity during the Holocene by means of LLMZA of Cave Flowstone.- Communications of the Int. Symp. on Phys.,Chem & Hydrogeological Research. of Karst, May 10-15, 1988, pp.97-100
Shopov Y.Y.,1989a, Bases and Structure of the International Programme "Luminescence of Cave Minerals" of the Commission of Physical Chemistry and Hydrogeology of Karst of UIS.-Exped. Annual of Sofia University, v.3/4,pp.111- 127.
Shopov Y.Y.,1989-b, Spectra of Luminescence of Cave Minerals, -Expedition Annual of Sofia University,v. 3/4,pp.80-85.
Shopov Y.Y.,Georgiev L.N.(1989) CS- Spectrophotometry- A New Method for Direct Registration of Spectra of Variable Processes.- Abstracts of XXVI Colloquium Spectroscopicum Internationale, 3-7 July 1989, Sofia, Bulgaria, v.III, p.194
Shopov Y.Y.,Dermendjiev Vl.(1990)Microzonality of Luminescence of Cave Flowstones as a New Indirect Index of Solar Activity.- Comptes rendus de l'Academie bulgare des Sci., v.43,7,pp.9-12.
Shopov Y.Y,Dermendjiev V, Buyukliev G., 1991a, A New Method for Dating of Natural Materials with Periodical Macrostructure by Autocalibration and its Application for Study of the Solar Activity in the Past.- Quaderni del Dipartimento di Geografia,n.13 Universita di Padova, pp.23- 30; IGCP 299 Newsletter, v.3, p.36- 41.
Shopov Y.Y.,Ford D.C.,Morrison J.,Schwarcz H.P.,Georgiev L.N., Sanambria M.E.,Dermendjiev V.,Buyukliev G.(1992) High resolution records of Quaternary Solar Activity,Climate and Variations- GSA Abstr., 1992, p.268.
Shopov Y.Y.,Ford D.C., Schwarcz H.P.(1994a) Luminescent Microbanding in speleothems: High resolution chronology and paleoclimate.- Geology, v.22, p.407 -410, May 1994.
Shopov Y.Y., L.Tsankov, L.N.Georgiev, A.Damyanova, Y. Damyanov, D.C. Ford, C.J.Yonge, W. MacDonald, H.P.R.Krouse (1996-a) Speleothems as Natural Climatic Stations with Annual to Daily Resolution- Extended abstracts of Int. Conference on "Climatic Change- the Karst Record", 1- 4 August 1996, Bergen, Norway. Karst Waters Institute Special Publication 2., p. 150-151.
Shopov Y.Y., L.Tsankov, L.N.Georgiev, A.Damyanova, Y. Damyanov, E. Marinova, D.C. Ford, C.J.Yonge, W. MacDonald, H.P.R.Krouse (1996-c) Speleothem Luminescence proxy Records of Annual Rainfall in the Past. Evidences for "The Deluge" in Speleothems."- Extended abstracts of Int. Conference on "Climatic Change- the Karst Record", 1- 4 August 1996, Bergen, Norway. Karst Waters Institute Special Publication 2., p. 155-156.
Shopov Y.Y., L.Tsankov, M. Buck, D.C.Ford (1996-d) Time Resolved Photography of Phosphorescence- A New Technique for Study of Thermal History and Uplift of Thermal Caves.- Extended abstracts of Int. Conference on "Climatic Change- the Karst Record", 1- 4 August 1996, Bergen, Norway. Karst Waters Institute Special Publication 2., p. 154.
Shopov Y.Y. (1997) Luminescence of Cave Minerals- in book: "Cave Minerals of the world" second edition, ed by C.Hill, P. Forti, NSS, Huntswille, Alabama, USA, pp.244-248
Slacik, J.: Vestn. Ustredn. Ustavu Geol. 1976,v.51, p. 107-112.
White W.B, Brennan E.S.(1989) Luminescence of speleothems due to fulvic acid and other activators.- Proceedings of 10th International Congress of Speleology, 13-20 August 1989, Budapest, v.1, pp.212- 214.

Further reading
Gorobets B.S.: Atlas of Spectra of Luminescence of Minerals.VIMS 1981,Moskow, 153 pp. (in Russian)
Tarashtan A.N., 1978, Luminescence of minerals. Naukova Dumka, Kiev,296 pp.(in Russian)