Interaction Between the ENSO and the Asian Monsoon in a Coral Record of Tropical Climate

Abstract

The oxygen isotopic composition of a banded coral from the western equatorial Indian Ocean provides a 150-year-long history of the relation between the El Niiio-Southern Oscillation (ENSO) phenomenon and the Asian monsoon. Interannual cycles in the coral time series were found to correlate with Pacific coral and instrumental climate records, suggesting a consistent linkage across ocean basins, despite the changing frequency and amplitude of the ENSO. However, decadal variability that is characteristic of the monsoon system also dominates the coral record, which implies important interactions between tropical and midlatitude climate variability. One prominent manifestation of this interaction is the strong amplitude modulation of the quasi-biennial cycle.Compilations of sea surface temperature (SST) anomalies demonstrate that the ENS0 phenomenon is equally important in both the Indian and Pacific oceans, which implies a climate connection over much of Earth (I ). However, the different basinal geometry and the seasonally reversing monsoon currents demand a separate set of physical processes governing interannual temperature variability in the Indian Ocean (2), and, therefore, the degree of coupling between the ocean basins-a central issue for predictability-is not necessarily fixed. In fact, the tendency for this coupling to evolve may explain why the relation between the ENS0 and the Asian monsoon has been the subject of one of the longest standing debates in climatology (3).Previous analyses have variously concluded either that the Asian monsoon affects the ENS0 or that the converse is true (4). Each of these conclusions allows the possibility for different large-scale feedbacks [for example, the former view implies that Eurasian snow cover could influence tropical climate (31. Yet, resolution of these dynamical effects with the instrumental record alone is compromised by the fact that continuous reliable observations rarely span more than three decades-a period areuablv alreadv modified bv human activitgs. %us, it isdifficult to predict whether the relations determined from modem observations would apply in basic climate states different from those of recent years. Furthermore, the long records that do exist (for example, the India Monsoon Rainfall Index) may not be the most appropriate measures of the large-scale Asian monsoon phenomenon (3). Defining the interaction between the ENS0 and the Asian monsoon requires not only an extended record but also a globally relevant index.

Decadal-scale variability of warm season temperature in Beijing over the past 2650 years

“…However, the presence of such climate signals in the Beijing temperature record clearly indicates the impacts of ocean-atmosphere interactions in modulating the decadal variability of summer temperature in the mid-latitudes. This interpretation is supported by modern observations [32][33][34][35][36], consistently showing the influences of tropical SST on the East Asian monsoon climate.…”

Indian Ocean Dipole index recorded in Kenyan coral annual density bands

“…[16] In the Indian Ocean, the effect of ENSO to SST and precipitation has been discussed [Reason et al, 2000], and found in coral band analysis [Charles et al, 1997;Cole et al, 2000]. While independent influence of IOD is recently discussed .…”

“…[2] Variability in the tropical and subtropical climate in the Pacific and Indian oceans has often been explained by the variability in the El Niño Southern Oscillation (ENSO) [Charles et al, 1997;Cole et al, 2000]. However, correlation between ENSO and climate variability in the Indian Ocean is not always high [Zinke et al, 2005].…”

“…In the western Indian Ocean, however, the coral record has largely been discussed in relation to ENSO variability. Charles et al [1997] analyzed a 150-year coral core from the Seychelles, and Cole et al [2000] examined a 194-year coral core from Kenya. Recently, two longer cores from Madagascar [Zinke et al, 2004] and Tanzania [Damassa et al, 2006] have also shown ENSO-like variation going back to the 17th century.…”

Atmosphere–ocean dynamics in the Western Indian Ocean recorded in corals

“…The corals precisely record the depletion in δ 18 O sea water during the NE monsoon season by showing negative δ 18 O anomalies ( figure 3). There is a high correlation between mean December-March coral δ 18 O, precipitation and outgoing long-wave (Reynolds & Smith 1994) between 1982(Charles et al . 1997).…”