Planktic foraminifera, particle flux and oceanic productivity off Pakistan, NE Arabian Sea: modern analogues and application to the palaeoclimatic record

Abstract

We use the flux of bulk sediment (CaC03, biogenic opal, organic carbon, lithogenic material), and of planktic foraminifera (PF) and other shell-bearing plankton from sediment trap EPT-2 off Pakistan to (1) constrain the seasonal pattern of regional productivity and (2) search for indications of the NE monsoon winter situation that may serve as a modem analogue to better reveal the seasonal climatic signals preserved in the sedimentary record of the Arabian Sea. Our trap data show a clear seasonality of fluxes that can also be traced in the composition of non-bioturbated (varved) summer and winter sediment laminae preserved within the oxygen minimum zone. In EPT-2, the flux of PF is low during summer, but during winter and late spring it is higher, as at trap station WAST, in the upwelling area of the western Arabian Sea. Globigerina bulloides, a PF species linked to summer upwelling and high productivity, is of minor importance off Pakistan. In contrast, Globigerina falconensis dominates in flux and relative abundance, and is indicative of winter mixing, when NE monsoonal winds cool the highly saline surface waters and break up stratification. An enhanced horizontal flux of suspended sediments stirred up on the shelf and upper slope is clearly shown by the peak in occurrence of small benthic foraminifera during winter. Altogether, our data suggest that the particle flux in the northeastern Arabian Sea is determined by local sediment resuspcnsion and winter productivity rather than by summer monsoonal upwelling, representing a 'nonupwelling' environment, in contrast to the 'summer upwelling' regime off Oman, Somalia and southern India. We used this evidence to reconstruct the seasonal intensity of both monsoons for the past 25 ka: the SW and NE monsoon both were weak during the last glacial period. The NE monsoon peaked during the cool phases of the glacial to interglacial climatic transition (i.e. during the Younger Dryas (YD) and Heinrich Event Hl). The SW monsoon was reinforced after the YD. Both monsoons were enhanced during early Holocene time, when summer insolation and hence atmospheric forcing was at a maximum.

Predicting the global distribution of planktonic foraminifera using a dynamic ecosystem model

“…To compare the modeled and observed annual distribution of the different planktonic foraminifera species we used those datasets with a minimum collecting period of one year and at least monthly resolution. We extended the database ofZarić et al (2005,2006) by adding trap data from the northwest Pacific Xu et al, 2005), Bering Sea (Asahi and Takahashi, 2007), South China Sea (Tian et al, 2005) and Arabian Sea (Schulz et al, 2002). Table 2 summarizes locations, details and references of the sediment-trap studies used in this study.…”

Terrigenous plant wax inputs to the Arabian Sea: Implications for the reconstruction of winds associated with the Indian Monsoon

“…Tindale and Pease, 1999;Sirocko et al, 2000). Satellite, sediment trap, and surface sediment data have demonstrated that the northeast monsoon does not transport significant quantities of dust to the Arabian Sea (Sirocko and Sarnthein, 1989;Clemens, 1998;Schulz et al, 2002). However, plant wax accumulation rates at sites affected by northeast monsoon winds are lower than at sites affected by the southwest monsoon winds and roughly equal to those at sites affected by the northwesterly winds.…”

Sensitivity of Red Sea circulation to sea level and insolation forcing during the last interglacial

“…The observed dominance of G. glutinata in the central Red Sea (see also Fenton, 1998) is unique, since highest G. glutinata abundances in the Red Sea are today observed only in the very south (Auras-Schudnagies et al, 1989;. G. glutinata occurs in general in productive regions (Cullen and Prell, 1984;Naidu and Malmgren, 1996;Schulz et al, 2002;Storz et al, 2009), suggesting that the cause of this increase is indeed linked to productivity, as indicated by our transfer function results, although absolute values have to be taken with care due to non-analogue conditions (Fig. 5).…”

“…The increasing productivity trend continues, following the increase in G. glutinata and decrease in G. sacculifer, until chlorophyll-a values return to modern conditions in KL9 at ∼110 ka BP. Absolute values between 121-112 ka BP are not reliable due to the lack of present day faunal analogues, but the high abundance of G. glutinata indicates that productivity was higher than today and during the Holocene in the central Red Sea, as this species is often associated with elevated productivity (Cullen and Prell, 1984;Naidu and Malmgren, 1996;Schulz et al, 2002).…”