Changes In Monsoon Strength Research Articles

Constraining Plio‐Pleistocene Shifts in Northwest African Hydroclimate, Ecosystem Distributions, and Marine Productivity: New Paleo‐Records Across the Mid‐Pleistocene Transition

AbstractNorthwest Africa transitioned from a wet/vegetated landscape toward drier/sparser conditions sometime between the late‐Pliocene and the late‐Pleistocene. However, our understanding of the precise timing and nature of this transition is hampered by a paucity of paleo‐records which bridge these two intervals. Here we report new plant‐wax isotope as well as dust and opal flux records from the relatively brief interval ∼1.1–1.0 million years ago (Ma) to evaluate the astronomical timescale controls of Northwest African hydroclimate and vegetation during the Mid‐Pleistocene Transition (MPT) and, in context with published records, the drivers of long‐term climate and ecological trends over the Plio‐Pleistocene. The tempo and amplitude of the Northwest African monsoon rainfall swings closely track low latitude insolation forcings over the last 5 Ma. However, we demonstrate that a pronounced mean state decline in monsoon strength likely occurred following the MPT most likely instigated by increasing Atlantic meridional sea surface temperature gradients or declines in the strength of the meridional overturning circulation. The northward extent of vegetation does not track changes in monsoon strength over the Plio‐Pleistocene and thus may be more strongly influenced by changes in monsoon rainfall extent or ecosystem disturbances. Progressively diminished dust fluxes following a decline in monsoon strength after 1.0 Ma is consistent with reduced production and subsequent depletion of fine‐grained sediments in the Sahara. Synchroneity between dust and opal fluxes across timescales suggests nutrient delivery to the surface ocean via dust plays a key role in marine primary productivity off the coast of Northwest Africa.

A strong influence of the mid-Pleistocene transition on the monsoon and associated productivity in the Indian Ocean

The short-term variability in the Indian monsoon is well documented through instrumental records and paleoclimatic studies of the recent geological past. However, the effect of mid-Pleistocene transition (MPT) on the Indian monsoon has not been discussed extensively due to the scarcity of long-term records of changes in monsoon strength. We have used a 1.45 myr record of planktic foraminifera assemblages from the Site U1446 to understand the effect of the MPT on monsoon and associated processes. From the variability in the abundance of the summer monsoon assemblage, it is evident that the Indian summer monsoon (ISM) was stronger during the warm interstadials and weaker during the stadials, whereas the winter monsoon assemblage suggests a weakened winter monsoon during the interstadials. From the variation in eutrophic assemblage, it is inferred that, throughout the studied interval, productivity was controlled by the ISM. We report a large-scale reorganization of the Indian monsoon system after the onset of the MPT, which resulted in the strengthening of ISM. We also report that during the post MPT period, the summer monsoon was influenced by the 23 kyr precession cycle and the 100 kyr eccentricity cycle strongly modulated the winter monsoon.

Dual response of Arabian Sea cyclones and strength of Indian monsoon to Southern Atlantic Ocean

Variability and trends of the south Asian monsoon at different time scales makes the region susceptible to climate-related natural disasters such as droughts and floods. Because of its importance, different studies have examined the climatic factors responsible for the recent changes in monsoon strength. Here, using observations and climate model experiments we show that monsoon strength is driven by the variations of south Atlantic Ocean sea surface temperature (SASST). The mechanism by which SASST is modulating the monsoon could be explained through the classical Matsuno-Gill response, leading to changes in the characteristics of vertical wind shear in the Arabian Sea. The decline in the vertical wind shear to the warming of SASST is associated with anomalous lower (upper)-level easterlies (westerlies). This further leads to a strong increase in the frequency of the Arabian Sea cyclones; and also prohibits the transport of moisture to the Indian landmass, which eventually reduces the strength of monsoon. The conditions in the SASST which drove these responses are aggravated by greenhouse gas emission, revealing the prominent role played by anthropogenic warming. If, with proper mitigation, these emissions are not prevented, further increases in the SASST is expected to result in increased Arabian sea cyclones and reduced monsoon strength.

Asian monsoon dynamics and sediment transport in SE Asia

The Asian monsoon is the dominant climatic phenomenon in Southeast Asia, responsible for most of the regional precipitation. As well as tectonics, climate is well recognized as a primary control on erosion and the transport of sediment to the ocean. Sediment records from the South China Sea show that strong monsoons are associated with intensified reworking of pre-existing floodplain sediments over millennial timescales. Strong monsoons result in deposition of more altered material that is also delivered at higher rates than during more arid times. Millennial-scale changes in monsoon strength result in changes in the weathering regime but not fast enough to account for the changes seen in the sediments preserved in Asian deltas. Instead monsoon modulated recycling dominates. Over longer time periods (>106 y) strengthening of the monsoon is linked to faster bedrock erosion and increased sediment flux of the ocean. Although this also has an effect on chemical weathering, on long time periods the monsoon is seen to be subsidiary to the effects of global cooling at least since the middle Miocene.

Climate modulation of summer rainstorm activity in eastern China based on the Tibetan Plateau spring heating

Rainstorm intensity and frequency in eastern China are closely associated with the Asian summer monsoon, one of the largest and most pronounced circulation systems on Earth. Changes in monsoon strength are linked to mechanical and thermal forcing by the Tibetan Plateau (TP), which, as an extensive elevated landmass, forms a vast heat source that protrudes into the free atmosphere. However, the impact of TP heating variability on rainstorm behavior in eastern China remains unclear. By analyzing 50 years of climate data, significant interannual variability was identified in the occurrence of rainstorms (precipitation amounts of > 50 mm), with decreased trend in northern China and increased variability in southern China. Results show that these changes are closely related with the springtime TP heating, indicating that recent changes in rainstorm distributions in eastern China are consistent with interdecadal variability in TP thermal forcing.

East Asian hydroclimate modulated by the position of the westerlies during Termination I.

Speleothem oxygen isotope records have revolutionized our understanding of the paleo East Asian monsoon, yet there is fundamental disagreement on what they represent in terms of the hydroclimate changes. We report a multiproxy speleothem record of monsoon evolution during the last deglaciation from the middle Yangtze region, which indicates a wetter central eastern China during North Atlantic cooling episodes, despite the oxygen isotopic record suggesting a weaker monsoon. We show that this apparent contradiction can be resolved if the changes are interpreted as a lengthening of the Meiyu rains and shortened post-Meiyu stage, in accordance with a recent hypothesis. Model simulations support this interpretation and further reveal the role of the westerlies in communicating the North Atlantic influence to the East Asian climate.

East Asian monsoon mysteries

Paleoclimatology What exactly does the oxygen isotopic composition of speleothems tell us about the East Asian monsoon? They provide magnificent, detailed records of hydroclimate, but precisely what aspects of hydroclimate they record is unclear. Zhang et al. present data from two speleothems from central eastern China for the period from 21,000 to 10,000 years ago and suggest that the cause of the oxygen isotopic variability that they observe is more complex than simple changes in monsoon strength or intensity (see the Perspective by McGee). Alternatively, this variation may reflect the lengths of various phases of the monsoon and the regional heterogeneity of the East Asian hydroclimate. Science , this issue p. [580][1]; see also p. [518][2] [1]: /lookup/doi/10.1126/science.aat9393 [2]: /lookup/doi/10.1126/science.aav5280

Wolfe Creek Crater: A continuous sediment fill in the Australian Arid Zone records changes in monsoon strength through the Late Quaternary

A bolide that impacted NW Australia during the Late Quaternary left a circular depression more than 100 m deep and nearly a kilometer in diameter, with a crater rim ∼30 m above the regional terrain. The resultant crater is a window into the regional water table. The surface of the contemporary central pan is 25 m below the adjacent terrain, coincident with the late Holocene regional water table modified by local evaporative processes. Shielded from aeolian deflation by the crater rim, the central depression has slowly filled with dust, sand, and chemical precipitates, estimated to be 20–100 m thick based on geophysical surveys, one of the few continuous depocenters in the Australian Arid Zone. The nature of the crater's sediment fill is controlled by interactions between the water table, primarily in response to changes in summer monsoon rain, changes in the delivery of sand and dust to the crater by the prevailing easterly winds, and the level of the sedimentary fill surface. Optically Stimulated Luminescence (OSL) and 14C dates constrain an age model indicating the upper 10 m of sediment fill recovered from the central pan span the past ∼60 ka. The lowest 3 m consist of clayey sand deposited in perennial water during Marine Isotope Stage (MIS) 3. The water table subsequently dropped rapidly ∼35 ka and remained more than 7 m below the late Holocene level through most of MIS 2, during which 2 m of sandy clay was deposited on a dry crater floor, confirming a dry and dusty Last Glacial Maximum (LGM) climate. By 14 ka a rising water table intersected the crater surface, modifying the upper 50 cm of LGM sediment, and syndepositionally modifying another 60 cm of subsequent sandy clay deposition. Aeolian sediment delivery effectively ceased ∼13 ka, and the upper 4.8 m is a gypsum-dominated precipitate, which initially accumulated rapidly, before equilibrating with the late Holocene water table shortly after 6 ka. Lacustrine carbonate encrustations on rocks at the base of the crater wall and ∼4 m above the central pan with 14C ages >40 ka document a time when regional groundwater maintained a water body in the crater 3.5–4.5 m above the modern groundwater level. The crater wall deflected the prevailing easterly winds, creating a horseshoe-dune extending westerly on both sides of the crater, with an extension rate of 35 m ka−1. An augered hole through the northern dune revealed 10 m of sediment overlying ferricrete. The lowest meter is a mixture of broken ferricrete and sand that we interpret to be debris from the bolide impact. Three OSL dates through the dune project an age for the debris-dune contact of 120 ± 10 ka. Changes in physical properties and bulk sediment δ13C through the 9 m of aeolian sediment indicate the lowest 1.8 m was deposited during MIS 5 (120–85 ka), under a uniformly wetter climate than present. The overlying 4.3 m of sediment was deposited between 85 and 14 ka (MIS 4, 3, 2) and exhibits transitional characteristics between the lower unit and the upper 3.8 of sand, which was deposited primarily during the Holocene. Large changes in the regional water table occurred over the past 60 ka, including an LGM water table persistently ≥7 m lower than late Holocene levels, and 3.5–4.5 m higher prior to 40 ka, plausibly in MIS 5, indicative of a stronger Australian Summer Monsoon than at any time subsequently. Age models and sediment properties from the two sedimentary records indicate the crater was formed >60 ka and most likely ∼120 ka, more recently than previous estimates.

Abrupt changes in Indian summer monsoon strength during 33,800 to 5500 years B.P.

AbstractSpeleothem proxy records from northeastern (NE) India reflect seasonal changes in Indian summer monsoon strength as well as moisture source and transport paths. We have analyzed a new speleothem record from Mawmluh Cave, Meghalaya, India, in order to better understand these processes. The data show a strong wet phase 33,500–32,500 years B.P. followed by a weak/dry phase from 26,000 to 23,500 years B.P. and a very weak phase from 17,000 to 15,000 years B.P. The record suggests abrupt increase in strength during the Bølling‐Allerød and early Holocene periods and pronounced weakening during the Heinrich and Younger Dryas cold events. We infer that these changes in monsoon strength are driven by changes in temperature gradients which drive changes in winds and moisture transport into northeast India.

Climate variability over the last two millennia in the North American Monsoon region, recorded in laminated lake sediments from Laguna de Juanacatlán, Mexico

High-resolution titanium (Ti) data obtained using an ITRAX XRF core scanner from a laminated sediment core from the Laguna de Juanacatlán, western central Mexico yield a unique high-resolution record of runoff (precipitation) change for the last 2000 years. In the absence of reliable, long-term meteorological records, comparison of the Ti data with information from the rich Spanish colonial period archives and the post-Independence period, confirms that Ti is a proxy for runoff. This interpretation is supported by comparison with other high-resolution archives from the surrounding region, primarily tree rings and other lake sediment sequences. The Juanacatlán Ti record is therefore a proxy for summer, monsoonal rainfall. The record provides new evidence from the Pacific margin of tropical North America of the occurrence of dry conditions through much of the Classic period ( c. AD 300—900), and wetter conditions during the later Medieval period ( c. AD 1200—1350). The period commonly known as the ‘Little Ice Age’ (LIA) shows considerable variability, with dry conditions in the early part ( c. AD 1400—1600) and wetter conditions, punctuated by multiyear droughts through the eighteenth century. A notable feature of the record is the apparent decoupling of lacustrine sedimentation from the climate since the mid-twentieth century, possibly resulting from anthropogenic disturbance. Preliminary interpretations of the Ti record indicate that patterns are consistent with changes in monsoon strength associated with ENSO and solar forcing over the last two millennia.

Coordinated hydrological regimes in the Indo-Pacific region during the past two millennia

Instrumental data suggest that major shifts in tropical Pacific atmospheric dynamics and hydrology have occurred within the past century, potentially in response to anthropogenic warming. To better understand these trends, we use the hydrogen isotopic ratios of terrestrial higher plant leaf waxes ( delta D-wax) in marine sediments from southwest Sulawesi, Indonesia, to compile a detailed reconstruction of central Indo-Pacific Warm Pool (IPWP) hydrologic variability spanning most of the last two millennia. Our paleodata are highly correlated with a monsoon reconstruction from Southeast Asia, indicating that intervals of strong East Asian summer monsoon (EASM) activity are associated with a weaker Indonesian monsoon (IM). Furthermore, the centennial-scale oscillations in our data follow known changes in Northern Hemisphere climate ( e. g., the Little Ice Age and Medieval Warm Period) implying a dynamic link between Northern Hemisphere temperatures and IPWP hydrology. The inverse relationship between the EASM and IM suggests that migrations of the Intertropical Convergence Zone and associated changes in monsoon strength caused synoptic hydrologic shifts in the IPWP throughout most of the past two millennia.

Detecting human impacts on the flora, fauna, and summer monsoon of Pleistocene Australia

Abstract. The moisture balance across northern and central Australia is dominated by changes in the strength of the Australian Summer Monsoon. Lake-level records that record changes in monsoon strength on orbital timescales are most consistent with a Northern Hemisphere insolation control on monsoon strength, a result consistent with recent modeling studies. A weak Holocene monsoon relative to monsoon strength 65–60 ka, despite stronger forcing, suggests a changed monsoon regime after 60 ka. Shortly after 60 ka humans colonized Australia and all of Australia's largest mammals became extinct. Between 60 and 40 ka Australian climate was similar to present and not changing rapidly. Consequently, attention has turned toward plausible human mechanisms for the extinction, with proponents for over-hunting, ecosystem change, and introduced disease. To differentiate between these options we utilize isotopic tracers of diet preserved in eggshells of two large, flightless birds to track the status of ecosystems before and after human colonization. More than 800 dated eggshells of the Australian emu (Dromaius novaehollandiae), an opportunistic, dominantly herbivorous feeder, provide a 140-kyr dietary reconstruction that reveals unprecedented reduction in the bird's food resources about 50 ka, coeval in three distant regions. These data suggest a tree/shrub savannah with occasionally rich grasslands was converted abruptly to the modern desert scrub. The diet of the heavier, extinct Genyornis newtoni, derived from >550 dated eggshells, was more restricted than in co-existing Dromaius, implying a more specialized feeding strategy. We suggest that generalist feeders, such as Dromaius, were able to adapt to a changed vegetation regime, whereas more specialized feeders, such as Genyornis, became extinct. We speculate that ecosystem collapse across arid and semi-arid zones was a consequence of systematic burning by early humans. We also suggest that altered climate feedbacks linked to changes in vegetation may have weakened the penetration of monsoon moisture into the continental interior, explaining the failure of the Holocene monsoon. Climate modeling suggests a vegetation shift may reduce monsoon rain in the interior by as much as 50%.

Fluvio–sedimentary response of the monsoon-fed Indian rivers to Late Pleistocene–Holocene changes in monsoon strength: reconstruction based on existing 14C dates

The primary objective of the present study is to identify major phases of alluviation in the Indian region since the abrupt Deglacial intensification of the monsoon (∼15 cal ka BP) on the basis of analysis of 68 radiocarbon dates from two major hydro-geomorphic regions of India: the Central Ganga Basin (CGB) and the Deccan Peninsula (DP). The recognition of main phases of alluviation and incision has been achieved by evaluating the temporal distribution and clustering of the radiocarbon dates from alluvial sequences. The clusters were detected on the basis of the interpretation of the summed probability distribution plots derived by using OxCal version 4.0.1 and CALPAL (version May 2006) software packages. The summed probability plots reveal that periods of alluviation in the CGB, represented by three clusters (13.9–12.3, 11.9–11.2 and 9.8–9.0 cal ka BP) occur roughly before the onset of Early Holocene monsoon optimum phase. Two other clusters occur in the intervals 3.6–2.8 and 1.1–0.9 cal ka BP. The peak monsoon period generally lacks clusters of radiocarbon dates implying fluvial erosion and channel incision. This period also shows clustering of radiocarbon dates of the abandoned channels. In comparison, 14C dates from DP alluvial units form clusters at 16.4–14, 12.8–11.2, 10.8–8.9, 8.1–6.7 and 5.1–3.9 cal ka BP, indicating an association with the Deglacial–Early Holocene humid phase. Alluviation in the DP appears to have continued, more or less, uninterrupted till the middle of the Holocene epoch. The beginning and end of the discernible gap in the radiocarbon dates of CGB (9.0–3.6 cal ka) broadly corresponds with the two well-established short-term events of the Holocene, 8.2 and 4.2 ka cal BP. In comparison, the prominent gap of DP radiocarbon dates (3.9–2.1 ka cal BP) approximately begins with the 4.2 ka cal BP short-term event (onset of aridity) and ends with the 2.0 ka cal BP enhanced monsoon event. Notwithstanding the inter-regional differences in the fluvio–sedimentary response in the India region, the clusters of radiocarbon dates indicate that the century to millennium scale variations in fluvial activity in the Indian subcontinent were intimately linked to long-term fluctuations in the monsoon strength during the Late Quaternary.

Indian Monsoon Variability in a Global Warming Scenario

The Intergovernmental Panel on Climate Change (IPCC) constituted by the World Meteorological Organisation provides expert guidance regarding scientific and technical aspects of the climate problem. Since 1990 IPCC has, at five-yearlyintervals, assessedand reported on the current state of knowledge and understanding of the climate issue. These reports have projected the behaviour of the Asian monsoon in the warming world. While the IPCC Second Assessment Report (IPCC, 1996) on climate model projections of Asian/Indian monsoon stated ``Most climate models produce more rainfall over South Asia in a warmer climate with increasing CO2'', the recent IPCC (2001) Third Assessment Report states ``It is likely that the warming associated with increasing greenhouse gas concentrations will cause an increase in Asian summer monsoon variability and changes in monsoon strength.'' Climate model projections(IPCC, 2001) also suggest more El Nino – like events in the tropical Pacific, increase in surface temperatures and decrease in the northern hemisphere snow cover. The Indian Monsoon is an important component of the Asian monsoon and its links with the El Nino Southern Oscillation (ENSO) phenomenon, northern hemisphere surface temperature and Eurasian snow are well documented. In the light of the IPCC globalwarming projections on the Asian monsoon, the interannual and decadal variability in summer monsoon rainfall over India and its teleconnections have been examined by using observed data for the 131-year (1871–2001) period. While the interannual variations showyear-to-year random fluctuations, thedecadal variations reveal distinct alternate epochs of above and below normal rainfall. The epochs tend to last for about three decades. There is no clear evidence to suggest that the strength and variability of the Indian Monsoon Rainfall (IMR) nor the epochal changes are affected by the global warming. Though the 1990s have been the warmest decade of the millennium(IPCC, 2001), the IMR variability has decreased drastically. Connections between the ENSO phenomenon, Northern Hemisphere surface temperature and the Eurasian snow with IMR reveal that the correlations are not only weak but have changed signs in the early 1990s suggesting that the IMR has delinked not only with the Pacific but with the Northern Hemisphere/Eurasian continent also. The fact that temperature/snow relationships with IMR are weak further suggests that global warming need not be a cause for the recent ENSO-Monsoon weakening. Observed snow depth over theEurasian continent has been increasing, which could be a result of enhanced precipitation due to the global warming.

On the late Pleistocene‐Holocene sapropel record of climatic and oceanographic variability in the eastern Mediterranean

Sapropels and intercalated marls in a piston core from the eastern Mediterranean are chemically and mineralogical distinct: kaolinite, smectite, and total S contents, Fe/A1, Ba/A1, Co/A1, Mo/A1, and V/A1 are higher, whereas quartz, Mg calcite, illite contents, Si/A1, Ti/A1, K/A1, Rb/A1, and Zr/A1 are lower in the sapropels. Missing and “ghost” sapropels are identified by mineralogical and chemical properties that are not prone to diagenesis. Primary production was higher (Ba/A1) and bottom water and/or interstitial oxygenation was lower (Co/A1, Mo/A1, Ni/A1, and V/A1) during sapropel formation. Wind speeds (quartz/clay, Si/A1, and Zr/A1) and bottom water salinities (Mg calcite/calcite) were higher during periods of marl formation. Sapropels represent a fundamentally different sedimentary facies whose formation is linked to changes in the hydrological balance in the basin, driven by precessionally modulated changes in monsoon strength and subtropical precipitation changes, which altered circulation, production, and sediment source areas.

Oxygen isotopes in lacustrine carbonates of West China revisited: implications for post glacial changes in summer monsoon circulation

Five lakes in the Qinghai–Tibet Plateau and North Xinjiang have provided oxygen isotope records covering the past 17–11 cal. kyr BP. The modern lakes are first presented within the major atmospheric circulation and climate patterns of China, with the climate-related isotope composition of input water. Equations used to extract hydrological and climatic information from δ 18O in carbonates are then given. After a discussion on potential causes for δ 18O changes, each of the five isotope profiles is interpreted in the light of its specific environmental data. The most significant event observed in all records occurred at 12–11 cal. kyr BP: an abrupt intensification of summer rainfall associated with an extremely rapid 1000–1500 km westward migration of the monsoon fronts. The monsoon regime weakened in stages after 8–7 cal. kyr BP. Holocene maximal aridity is recorded at all sites between about 4.5 and 3.5 cal. kyr BP. Long-term changes in monsoon strength as inferred from our isotopic interpretation are in good agreement with climate model reconstructions in the Tibet–Qinghai Plateau, while observed hydrological changes in North Xinjiang are not simulated by the models. Also, the non-linearity of the Holocene monsoon variations cannot be accounted for by orbital forcing.

Monsoons and the dynamics of deserts

AbstractThe existence of subtropical deserts, such as the Sahara, has often been attributed to the annual‐mean, zonal‐mean Hadley circulation which shows strong descent in the subtropics. However, the zonal‐mean Hadley circulation shows considerable evolution over the course of the year with very strong subtropical descent during winter, but practically no zonal‐mean subtropical descent during summer when rainfall over the eastern Sahara and the Mediterranean is least. Charney (1975) proposed a biosphere‐albedo feedback mechanism whereby local anthropogenic effects related to over‐grazing could affect the radiative balance, enhancing summertime diabatic descent and leading to desertification of the subtropics in general. The present study, which uses an idealized model, suggests a monsoon‐desert mechanism for desertification whereby remote diabatic heating in the Asian monsoon region can induce a Rossby‐wave pattern to the west. Integral with the Rossby‐wave solution is a warm thermal structure that interacts with air on the southern flank of the mid‐latitude westerlies causing it to descend. This adiabatic descent is localized over the eastern Sahara and Mediterranean, and over the Kyzylkum desert to the south‐east of the Aral Sea, by the mountains of north Africa and south‐west Asia. Trajectories indicate that the monsoon‐desert mechanism does not represent a simple ‘Walker‐type’ overturning cell. Instead, the descending air is seen to be mainly of mid‐latitude origin. It is speculated that the monsoon‐forced adiabatic descent may result in clear air and, therefore, a local diabatic enhancement which effectively doubles the strength of descent. With this mechanism, desertification can be forced by remote changes in monsoon strength rather than by local effects. This conclusion is supported by the observed dramatic strengthening of descent over the Mediterranean and east Sahara during the onset of the Asian monsoon and, on the longer timescale, by relating prehistoric lake‐levels to Milankovitch‐monsoon forcing. The latter may help to explain the perceived discrepancies between the palaeoclimate of the eastern Sahara and the strength of a ‘tropic‐wide’ monsoon. The monsoon‐desert mechanism may not be confined to the Asian monsoon alone and the existence of other monsoon‐climate regions over the globe may, in a similar way, explain the observed summertime strengthening of the oceanic sub‐tropical anticyclones and the existence of western continental deserts and ‘Mediterranean‐type’ climate regions.

Interhemispheric moisture transport in the Indian Ocean summer monsoon: Data‐model and model‐model comparisons

Exchange of energy and mass between the ocean and the atmosphere is an integral component of Indian Ocean summer‐monsoon dynamics. Most previous general circulation model simulations of the monsoon have prescribed sea surface temperature (SST), thus severely constraining atmosphere‐ocean energy exchanges. Here we compare model physics, based on both prescribed and computed SST simulations, to observed climate links between northern hemisphere monsoon strength and the cross‐equatorial transport of moisture (latent heat) from the southern subtropical Indian Ocean. For the computed SST case, stronger southern hemisphere southeast trades and colder southern subtropical SSTs are associated with increased cross‐equatorial moisture flux. Increased moisture flux induces strengthened monsoon circulation via increased condensational heating and decreased sea level pressure over Asia. For the prescribed SST case, stronger southeast trades and colder southern subtropical SSTs are also associated with increased cross‐equatorial moisture flux and, hence, strengthened monsoon circulation. However, in this case, the increased moisture flux is induced by strengthened cross‐equatorial winds associated with subsidence over the cold southern hemisphere SSTs (i.e., increased sea level pressure in the southern subtropics). Thus the model physics associated with changes in monsoon strength are very different for the prescribed and computed SST simulations. Only the computed SST simulation replicates observed meteorological relationships.