Influence of the intertropical convergence zone on early cretaceous plant distribution in the South Atlantic.
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ABSTRACT:
SUBMITTER: de A Carvalho M
PROVIDER: S-EPMC9308796 | biostudies-literature |
REPOSITORIES: biostudies-literature
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Project description:Most Atlantic hurricanes form in the Main Development Region between 9°N to 20°N along the northern edge of the Intertropical Convergence Zone (ITCZ). Previous research has suggested that meridional shifts in the ITCZ position on geologic timescales can modulate hurricane activity, but continuous and long-term storm records are needed from multiple sites to assess this hypothesis. Here we present a 3000 year record of intense hurricane strikes in the northern Bahamas (Abaco Island) based on overwash deposits in a coastal sinkhole, which indicates that the ITCZ has likely helped modulate intense hurricane strikes on the western North Atlantic margin on millennial to centennial-scales. The new reconstruction closely matches a previous reconstruction from Puerto Rico, and documents a period of elevated intense hurricane activity on the western North Atlantic margin from 2500 to 1000 years ago when paleo precipitation proxies suggest that the ITCZ occupied a more northern position. Considering that anthropogenic warming is predicted to be focused in the northern hemisphere in the coming century, these results provide a prehistoric analog that an attendant northern ITCZ shift in the future may again return the western North Atlantic margin to an active hurricane interval.
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Project description:We present early Cretaceous to present paleobathymetric reconstructions and quantitative uncertainty estimates for the South Atlantic, offering a strong basis for studies of paleocirculation, paleoclimate and paleobiogeography. Circulation in an initially salty and anoxic ocean, restricted by the topography of the Falkland Plateau, Rio Grande Ridge and Walvis Rise, favoured deposition of thick evaporites in shallow water of the Brazilian-Angolan margins. This ceased as seafloor spreading propagated northwards, opening an equatorial gateway to shallow and intermediate circulation. This gateway, together with subsiding volcano-tectonic barriers would have played a key role in Late Cretaceous climate changes. Later deepening and widening of the South Atlantic, together with gateway opening at Drake Passage would lead, by mid-Miocene (?15 Ma) to the establishment of modern-style thermohaline circulation.
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Project description:The position of the Intertropical Convergence Zone (ITCZ) is sensitive to changes in the balance of heat between the hemispheres which has fundamental implications for tropical hydrology and atmospheric circulation. Although the ITCZ is thought to experience the largest shifts in position during deglacial stadial events, the magnitude of shifts has proven difficult to reconstruct, in part because of a paucity of high-resolution records, particularly those including spatial components. Here we track the position of the ITCZ from 150 to 110?ka at three sites in the central equatorial Pacific at sub-millennial time resolution. Our results provide evidence of large, abrupt changes in tropical climate during the penultimate deglaciation, coincident with North Atlantic Heinrich Stadial 11 (?136-129?ka). We identify this event both as a Northern Hemisphere increase in aeolian dust and as a shift in the mean position of the ITCZ a minimum of 4° southwards at 160° W.
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Project description:Large changes in hydroclimate in the Neotropics implied by proxy evidence, such as during the Little Ice Age, have been attributed to meridional shifts of the intertropical convergence zone (ITCZ), although alternative modes of ITCZ variability have also been suggested. Here, we use seasonally resolved stalagmite rainfall proxy data from the modern northern limit of the ITCZ in southern Belize, combined with records from across the Neotropics and subtropics, to fingerprint ITCZ variability during the Common Era. Our data are consistent with models that suggest ITCZ expansion and weakening during globally cold climate intervals and contraction and intensification during global warmth. As a result, regions currently in the margins of the ITCZ in both hemispheres are likely transitioning to more arid and highly variable conditions, aggravating current trends of increased social unrest and mass migration.
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Project description:Purpose of reviewThe intertropical convergence zone (ITCZ) is a planetary-scale band of heavy precipitation close to the equator. Here, we consider the response of the ITCZ structure to climate change using observations, simulations, and theory. We focus on the substantial yet underappreciated projected changes in ITCZ width and strength, and highlight an emerging conceptual framework for understanding these changes.Recent findingsSatellite observations and reanalysis data show a narrowing and strengthening of precipitation in the ITCZ over recent decades in both the Atlantic and Pacific basins, but little change in ITCZ location. Consistent with observations, coupled climate models predict no robust change in the zonal-mean ITCZ location over the twenty-first century. However, the majority of models project a narrowing of the ITCZ and weakening mean ascent. Interestingly, changes in ITCZ width and strength are strongly anti-correlated across models.SummaryThe ITCZ has narrowed over recent decades yet its location has remained approximately constant. Climate models project further narrowing and a weakening of the average ascent within the ITCZ as the climate continues to warm. Following intense work over the last ten years, the physical mechanisms controlling the ITCZ location are now well understood. The development of complementary theories for ITCZ width and strength is a current research priority. Outstanding challenges include understanding the ITCZ response to past climate changes and over land versus ocean regions, and better constraining all aspects of the ITCZ structure in model projections.Electronic supplementary materialThe online version of this article (10.1007/s40641-018-0110-5) contains supplementary material, which is available to authorized users.
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Project description:The Intertropical Convergence Zone (ITCZ) encompasses the heaviest rain belt on the Earth. Few direct long-term records, especially in the Pacific, limit our understanding of long-term natural variability for predicting future ITCZ migration. Here we present a tropical precipitation record from the Southern Hemisphere covering the past 282,000 years, inferred from a marine sedimentary sequence collected off the eastern coast of Papua New Guinea. Unlike the precession paradigm expressed in its East Asian counterpart, our record shows that the western Pacific ITCZ migration was influenced by combined precession and obliquity changes. The obliquity forcing could be primarily delivered by a cross-hemispherical thermal/pressure contrast, resulting from the asymmetric continental configuration between Asia and Australia in a coupled East Asian-Australian circulation system. Our finding suggests that the obliquity forcing may play a more important role in global hydroclimate cycles than previously thought.
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Project description:The double-Intertropical Convergence Zone (ITCZ) problem, in which excessive precipitation is produced in the Southern Hemisphere tropics, which resembles a Southern Hemisphere counterpart to the strong Northern Hemisphere ITCZ, is perhaps the most significant and most persistent bias of global climate models. In this study, we look to the extratropics for possible causes of the double-ITCZ problem by performing a global energetic analysis with historical simulations from a suite of global climate models and comparing with satellite observations of the Earth's energy budget. Our results show that models with more energy flux into the Southern Hemisphere atmosphere (at the top of the atmosphere and at the surface) tend to have a stronger double-ITCZ bias, consistent with recent theoretical studies that suggest that the ITCZ is drawn toward heating even outside the tropics. In particular, we find that cloud biases over the Southern Ocean explain most of the model-to-model differences in the amount of excessive precipitation in Southern Hemisphere tropics, and are suggested to be responsible for this aspect of the double-ITCZ problem in most global climate models.
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Project description:The Intertropical Convergence Zone (ITCZ) is a salient feature of tropical atmospheric circulation characterized by intense convective clouds and rainfall north of the equator. Climate models, however, commonly experience the double-ITCZ problem-the tendency to produce another strong precipitation band but south of the equator. Here, we describe coupled interaction between the ITCZ and the North Equatorial Countercurrent (NECC) that is relevant to this problem. This current is a major component of the tropical Pacific upper-ocean circulation, which flows against easterly trade winds and transports warm water from the western Pacific eastward. Its core follows the latitudinal position of the ITCZ. Trade winds converge toward the ITCZ, creating a local minimum in zonal winds and generating positive wind stress curl that maintains an eastward current despite westward winds. We show that interaction between the ITCZ and the NECC involves positive feedback: a stronger NECC advects warm water from the western Pacific to the colder east thus increasing sea surface temperature (SST) along its path, intensifying convection within the ITCZ and hence strengthening wind stress curl, further strengthening the NECC. To demonstrate this wind stress curl-advection-SST-precipitation (WASP) feedback, we conduct climate model experiments in which we progressively strengthen the surface Ekman component of the NECC and observe the intensification of the ITCZ and the entire NECC. Consequently, a weak NECC leads to a weak ITCZ, which can contribute to the double-ITCZ problem in climate models, since weak wind convergence north of the equator enables stronger convergence in the south.
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Project description:The important role played by the upper plate in convergence zones dynamics has long been underestimated but is now more and more emphasized. However, the influence of its thickness and/or strength on orogenic systems evolution remains largely unknown. Here we present results from 3D thermo-mechanical numerical simulations of convergence zones (including oceanic subduction followed by continental subduction/collision), in which we vary the rheological profile of the overriding plate (OP). For this, we systematically modify the crustal thickness of the overriding lithosphere and the temperature at the Moho to obtain a thermal thickness of the overriding lithosphere ranging from 80 to 180 km. While all models share a common global evolution (i.e., slab sinking, interaction between slab and the 660 km discontinuity, continental subduction/collision, and slab breakoff), they also highlight first-order differences arising from the variations in the OP strength (thermal thickness). With a thin/weak OP, slab rollback is favored, the slab dip is low, the mantle flow above the slab is vigorous, and the trench migrates at a high rate compared to a thick/strong OP. In addition, slab breakoff and back-arc basin formation events occur significantly earlier than in models involving a thick OP. Our models therefore highlight the major role played by the thickness/strength of the OP on convergence zone dynamics and illustrate its influence in a quantitative way.
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