Dipole patterns in tropical precipitation were pervasive across landmasses throughout Marine Isotope Stage 5

Most of Earth’s rain falls in the tropics, often in highly seasonal monsoon rains, which are thought to be coupled to the inter-hemispheric migrations of the Inter-Tropical Convergence Zone in response to the seasonal cycle of insolation. Yet characterization of tropical rainfall behaviour in the geologic past is poor. Here we combine new and existing hydroclimate records from six large-scale tropical regions with fully independent model-based rainfall reconstructions across the last interval of sustained warmth and ensuing climate cooling between 130 to 70 thousand years ago (Marine Isotope Stage 5). Our data-model approach reveals large-scale heterogeneous rainfall patterns in response to changes in climate. We note pervasive dipole-like tropical precipitation patterns, as well as different loci of pre- cipitation throughout Marine Isotope Stage 5 than recorded in the Holocene. These rainfall patterns cannot be solely attributed to meridional shifts in the Inter-Tropical Convergence Zone

Dynamic responses of Indian Summer Monsoon variability during past warm intervals

The South Asian or Indian Summer Monsoon (ISM) is an iconic reflection of land-ocean-atmosphere inter- actions on Earth, affecting over a billion people. Future predictions of northern hemisphere monsoon rainfall are fraught with large uncertainties in the Intergovernmental Panel on Climate Change (IPCC) reports. To better understand monsoon rainfall pattern/behaviours in future, we need to investigate its response to cli- matic drivers, including past warm intervals. We present multi-proxy geochemical and vegetation records of monsoon variability from the Bay of Bengal using sediment sequences recovered during the Integrated Ocean Discovery Programme (IODP) expedition 353. We utilise these multi-proxy records to assess re- sponses of ISM dynamics to past warming by comparing Holocene and last interglacial warm intervals at sub-millennial timescale. We integrate proxies’ records and intermediate complexity climate model outputs to present evidence for heterogenous rainfall pattern across global tropical landmasses when comparing the Holocene and last interglacial warm intervals. We also find regional differences in monsoon rainfall pattern along with changing loci of the precipitation when comparing these warm intervals. Further, we will present results of seasonal rainfall variability extremes, inferred from continental and marine proxy data, covering cool and warm climate states of the late Pleistocene

Factors affecting consistency and accuracy in identifying modern macroperforate planktonic foraminifera

Planktonic foraminifera are widely used in biostratigraphic, palaeoceanographic and evolutionary studies, but the strength of many study conclusions could be weakened if taxonomic identifications are not reproducible by different workers. In this study, to assess the relative importance of a range of possible reasons for among-worker disagreement in identification, 100 specimens of 26 species of macroperforate planktonic foraminifera were selected from a core-top site in the subtropical Pacific Ocean. Twenty-three scientists at different career stages – including some with only a few days experience of planktonic foraminifera – were asked to identify each specimen to species level, and to indicate their confidence in each identification. The participants were provided with a species list and had access to additional reference materials. We use generalised linear mixed-effects models to test the relevance of three sets of factors in identification accuracy: participant-level characteristics (including experience), species-level characteristics (including a participant’s knowledge of the species) and specimen-level characteristics (size, confidence in identification). The 19 less experienced scientists achieve a median accuracy of 57 %, which rises to 75 % for specimens they are confident in. For the 4 most experienced participants, overall accuracy is 79 %, rising to 93 % when they are confident. To obtain maximum comparability and ease of analysis, everyone used a standard microscope with only 35× magnification, and each specimen was studied in isolation. Consequently, these data provide a lower limit for an estimate of consistency. Importantly, participants could largely predict whether their identifications were correct or incorrect: their own assessments of specimen-level confidence and of their previous knowledge of species concepts were the strongest predictors of accuracy

Remote and local drivers of Pleistocene South Asian summer monsoon precipitation: A test for future predictions

South Asian precipitation amount and extreme variability are predicted to increase due to thermodynamic effects of increased 21st-century greenhouse gases, accompanied by an increased supply of moisture from the southern hemisphere Indian Ocean. We reconstructed South Asian summer-monsoon precipitation and runoff into the Bay of Bengal to assess the extent to which these factors also operated in the Pleistocene, a time of large-scale natural changes in carbon dioxide and ice volume. South Asian precipitation and runoff are strongly coherent with, and lag, atmospheric CO2 changes at Earth-orbital eccentricity, obliquity, and precession bands and are closely tied to cross-equatorial wind strength at the precession band. We find that the projected monsoon response to ongoing, rapid high-latitude ice melt and rising CO2 levels is fully consistent with dynamics of the past 0.9 million years

Reconstructing the Indian Monsoon response to global climate change

The Indian Summer Monsoon, a subsystem of the Asian Monsoon, is one of Earth’s most dynamic expressions of oceanic atmospheric-terrestrial processes affecting some of Earth’s most densely populated regions. Therefore, it is imperative to have a comprehensive understanding of the Indian Summer Monsoon in order to understand how its behaviour may be manifested by anthropogenic induced climate changes. Reconstructing how the monsoon behaved in the past presents an opportunity to disentangle its sensitivities to a range of forcing parameters (e.g. ice volume) during periods of different climatic states. However, understanding of how the Indian Summer Monsoon behaved in the past has been limited both spatially and temporally, further constrained by discrepancies among climate proxy records. This thesis fills both a temporal and spatial gap in our knowledge of the past behaviour of the Indian Summer Monsoon. High-resolution (millennial scale) records of Indian Summer Monsoon induced river runoff and surface freshening from the core convective region of the Indian Summer Monsoon, the northern Bay of Bengal and Andaman Sea, have been generated from 140 to 70 thousand years ago. These records provide an insight into how the Indian Summer Monsoon responded to the penultimate deglaciation (Termination II), the subsequent warmth of the Last Interglacial Period and ensuing oscillations between warm interstadial and cold stadial periods of Marine Isotope Stage 5. These records are compared with both high-latitude and low-latitude climate records in order to understand how the monsoon responded to changes in Earth’s internal climate system and the influence of external forcing

IODP 353-U1448 bulk sediment elemental variations across Marine Isotope Stage 5

IODP 353-U1448 bulk sediment elemental variations (Ti, Ca, K, Al, Si, Rb, Sr, Zr, Mn, Fe) measured using portable-XRF across ~70-140 thousand years ago. Elemental variations have corresponding core depth (m) and assigned age (ka)

Indian Summer Monsoon multi-proxy records from the Bay of Bengal across Marine Isotope Stage 5

Multi-proxy records from two deep-sea sediment cores (IODP 353-U1446 and U1448) of the stable oxygen isotope composition (N. dutertrei) and trace element ratios (G. ruber ss, N. dutertrei) measured in planktic foraminifera, foraminiferal percent abundance and bulk sediment elemental variations gained from portable-XRF. These records are inferred to capture Indian Summer Monsoon river runoff across Marine Isotope Stage 5/6 (70-140 thousand years ago)

IODP Site 353-U1446 Mg/Ca, Mn/Ca, Nd/Ca, U/Ca, δ18O and δ13C records of Neogloboquadrina dutertrei across Marine Isotope Stage 5

IODP 353-U1448 trace element (Mg/Ca, Mn/Ca, Nd/Ca and U/Ca) and isotope (δ18O and δ13C) of planktic foraminifera Neogloboquadrina dutertrei across ~70-140 thousand years ago. The data have corresponding core depth (m) and assigned age (ka)

IODP Site 353-U1446 Mg/Ca, Mn/Ca, Nd/Ca, U/Ca, δ18O and δ13C records of Neogloboquadrina dutertrei across Marine Isotope Stage 5

IODP 353-U1446 trace element (Mg/Ca, Mn/Ca, Nd/Ca and U/Ca) and isotope (δ18O and δ13C) of planktic foraminifera Neogloboquadrina dutertrei across ~70-140 thousand years ago. The data have corresponding core depth (m) and assigned age (ka)