Arianna Valentina Del Gaudio

Understanding how the Earth’s system behaves under climate forcing conditions is critical for predicting how future climate change scenarios may affect the planet. In this regard, the Miocene, with an atmospheric temperature ~4 °C higher than modern and a near-modern ocean configuration, stands out as a potential analogue for future climate projections. Our current understanding of the Miocene derives principally from the Atlantic and Pacific Oceans, whereas the Indian Ocean remains understudied. Nevertheless, different studies performed in the equatorial Indian Ocean have revealed that the multiple climate shifts that occurred during the Miocene modified both the atmospheric and oceanic processes in this basin (e.g., changes in westerlies position, nutrient flux and productivity). In the present study, we investigate how changes in the climate conditions affected the surface ocean system at Ocean Drilling Program (ODP) Site 752, located in the southeastern Indian Ocean, across the Middle to Late Miocene. For this purpose, we present a new quantitative dataset of calcareous nannofossil assemblages, in conjunction with already existing multi-proxy data. Our results indicate that the warm atmospheric conditions reached during the Miocene Climatic Optimum (MCO), starting at ~16.9 Ma, caused an intensification of the seasonal signal at ODP Site 752 that lasted until 15.32 Ma. After this period, we detected a shift in the calcareous nannofossil assemblage towards species characteristic of low-nutrient and warm-water conditions (e.g., Reticulofenestra pseudoumbilicus, Reticulofenestra haqii). Nevertheless, with the progression towards the Late Miocene Cooling, which started at ~7 Ma, and the increased influence of the cooler and more productive Southern Ocean waters, the calcareous nannofossil assemblage evolved into a community characterised by relatively high-nutrient and cold-water taxa (e.g., Coccolithus pelagicus, Calcidiscus leptoporus). By 10.67 Ma, we recorded a reversion in the nannoplankton assemblage to species typical of low-nutrient and warm-water conditions that lasted until 9.88 Ma. The comparison with available eNd(t) records for Site 752 and 707 (located in the equatorial Indian Ocean) revealed that this change in the assemblage composition responded to a strengthening of the Pacific Ocean water influx occurring at this time. High-nutrient and cold-water conditions were reestablished after 9.88 Ma, lasting until the end of the studied record at ~7.34 Ma. Our evaluation of the primary producer community from a multi-proxy-based perspective revealed a progressive evolution of the surface ocean conditions in the southeastern Indian Ocean region across the Middle to Late Miocene for the first time. Furthermore, the strong correlation with existing proxy data for global climate records suggests that large-scale climate events are the main factors driving the changes in the primary producer community and surface ocean conditions at the Broken Ridge during the Middle to Late Miocene. However, certain regional processes (e.g., strengthening of the Pacific Ocean influx) may also occasionally influence surface ocean conditions. Moreover, this multi-proxy approach allowed us to better understand the Indian Ocean–Southern Ocean interaction, and more specifically, the nutrient transport efficiency between these two ocean basins during a climate change scenario. Specifically, our multi-proxy-based dataset revealed that the Antarctic divergence region experienced a northward migration after the MCO, leading to a deep reorganisation of nutrient transport across the surface southeastern Indian Ocean.

Understanding how the Earth’s system behaves under climate forcing conditions is critical for predicting how future climate change scenarios may affect the planet. In this regard, the Miocene, with an atmospheric temperature ~4 °C higher than modern and a near-modern ocean configuration, stands out as a potential analogue for future climate projections. Our current understanding of the Miocene derives principally from the Atlantic and Pacific Oceans, whereas the Indian Ocean remains understudied. Nevertheless, different studies performed in the equatorial Indian Ocean have revealed that the multiple climate shifts that occurred during the Miocene modified both the atmospheric and oceanic processes in this basin (e.g., changes in westerlies position, nutrient flux and productivity). In the present study, we investigate how changes in the climate conditions affected the surface ocean system at Ocean Drilling Program (ODP) Site 752, located in the southeastern Indian Ocean, across the Middle to Late Miocene. For this purpose, we present a new quantitative dataset of calcareous nannofossil assemblages, in conjunction with already existing multi-proxy data. Our results indicate that the warm atmospheric conditions reached during the Miocene Climatic Optimum (MCO), starting at ~16.9 Ma, caused an intensification of the seasonal signal at ODP Site 752 that lasted until 15.32 Ma. After this period, we detected a shift in the calcareous nannofossil assemblage towards species characteristic of low-nutrient and warm-water conditions (e.g., Reticulofenestra pseudoumbilicus, Reticulofenestra haqii). Nevertheless, with the progression towards the Late Miocene Cooling, which started at ~7 Ma, and the increased influence of the cooler and more productive Southern Ocean waters, the calcareous nannofossil assemblage evolved into a community characterised by relatively high-nutrient and cold-water taxa (e.g., Coccolithus pelagicus, Calcidiscus leptoporus). By 10.67 Ma, we recorded a reversion in the nannoplankton assemblage to species typical of low-nutrient and warm-water conditions that lasted until 9.88 Ma. The comparison with available eNd(t) records for Site 752 and 707 (located in the equatorial Indian Ocean) revealed that this change in the assemblage composition responded to a strengthening of the Pacific Ocean water influx occurring at this time. High-nutrient and cold-water conditions were reestablished after 9.88 Ma, lasting until the end of the studied record at ~7.34 Ma. Our evaluation of the primary producer community from a multi-proxy-based perspective revealed a progressive evolution of the surface ocean conditions in the southeastern Indian Ocean region across the Middle to Late Miocene for the first time. Furthermore, the strong correlation with existing proxy data for global climate records suggests that large-scale climate events are the main factors driving the changes in the primary producer community and surface ocean conditions at the Broken Ridge during the Middle to Late Miocene. However, certain regional processes (e.g., strengthening of the Pacific Ocean influx) may also occasionally influence surface ocean conditions. Moreover, this multi-proxy approach allowed us to better understand the Indian Ocean–Southern Ocean interaction, and more specifically, the nutrient transport efficiency between these two ocean basins during a climate change scenario. Specifically, our multi-proxy-based dataset revealed that the Antarctic divergence region experienced a northward migration after the MCO, leading to a deep reorganisation of nutrient transport across the surface southeastern Indian Ocean.

Understanding how the Earth’s system behaves under climate forcing conditions is critical for predicting how future climate change scenarios may affect the planet. In this regard, the Miocene, with an atmospheric temperature ~4 °C higher than modern and a near-modern ocean configuration, stands out as a potential analogue for future climate projections. Our current understanding of the Miocene derives principally from the Atlantic and Pacific Oceans, whereas the Indian Ocean remains understudied. Nevertheless, different studies performed in the equatorial Indian Ocean have revealed that the multiple climate shifts that occurred during the Miocene modified both the atmospheric and oceanic processes in this basin (e.g., changes in westerlies position, nutrient flux and productivity). In the present study, we investigate how changes in the climate conditions affected the surface ocean system at Ocean Drilling Program (ODP) Site 752, located in the southeastern Indian Ocean, across the Middle to Late Miocene. For this purpose, we present a new quantitative dataset of calcareous nannofossil assemblages, in conjunction with already existing multi-proxy data. Our results indicate that the warm atmospheric conditions reached during the Miocene Climatic Optimum (MCO), starting at ~16.9 Ma, caused an intensification of the seasonal signal at ODP Site 752 that lasted until 15.32 Ma. After this period, we detected a shift in the calcareous nannofossil assemblage towards species characteristic of low-nutrient and warm-water conditions (e.g., Reticulofenestra pseudoumbilicus, Reticulofenestra haqii). Nevertheless, with the progression towards the Late Miocene Cooling, which started at ~7 Ma, and the increased influence of the cooler and more productive Southern Ocean waters, the calcareous nannofossil assemblage evolved into a community characterised by relatively high-nutrient and cold-water taxa (e.g., Coccolithus pelagicus, Calcidiscus leptoporus). By 10.67 Ma, we recorded a reversion in the nannoplankton assemblage to species typical of low-nutrient and warm-water conditions that lasted until 9.88 Ma. The comparison with available eNd(t) records for Site 752 and 707 (located in the equatorial Indian Ocean) revealed that this change in the assemblage composition responded to a strengthening of the Pacific Ocean water influx occurring at this time. High-nutrient and cold-water conditions were reestablished after 9.88 Ma, lasting until the end of the studied record at ~7.34 Ma. Our evaluation of the primary producer community from a multi-proxy-based perspective revealed a progressive evolution of the surface ocean conditions in the southeastern Indian Ocean region across the Middle to Late Miocene for the first time. Furthermore, the strong correlation with existing proxy data for global climate records suggests that large-scale climate events are the main factors driving the changes in the primary producer community and surface ocean conditions at the Broken Ridge during the Middle to Late Miocene. However, certain regional processes (e.g., strengthening of the Pacific Ocean influx) may also occasionally influence surface ocean conditions. Moreover, this multi-proxy approach allowed us to better understand the Indian Ocean–Southern Ocean interaction, and more specifically, the nutrient transport efficiency between these two ocean basins during a climate change scenario. Specifically, our multi-proxy-based dataset revealed that the Antarctic divergence region experienced a northward migration after the MCO, leading to a deep reorganisation of nutrient transport across the surface southeastern Indian Ocean.

Understanding how the Earth’s system behaves under climate forcing conditions is critical for predicting how future climate change scenarios may affect the planet. In this regard, the Miocene, with an atmospheric temperature ~4 °C higher than modern and a near-modern ocean configuration, stands out as a potential analogue for future climate projections. Our current understanding of the Miocene derives principally from the Atlantic and Pacific Oceans, whereas the Indian Ocean remains understudied. Nevertheless, different studies performed in the equatorial Indian Ocean have revealed that the multiple climate shifts that occurred during the Miocene modified both the atmospheric and oceanic processes in this basin (e.g., changes in westerlies position, nutrient flux and productivity). In the present study, we investigate how changes in the climate conditions affected the surface ocean system at Ocean Drilling Program (ODP) Site 752, located in the southeastern Indian Ocean, across the Middle to Late Miocene. For this purpose, we present a new quantitative dataset of calcareous nannofossil assemblages, in conjunction with already existing multi-proxy data. Our results indicate that the warm atmospheric conditions reached during the Miocene Climatic Optimum (MCO), starting at ~16.9 Ma, caused an intensification of the seasonal signal at ODP Site 752 that lasted until 15.32 Ma. After this period, we detected a shift in the calcareous nannofossil assemblage towards species characteristic of low-nutrient and warm-water conditions (e.g., Reticulofenestra pseudoumbilicus, Reticulofenestra haqii). Nevertheless, with the progression towards the Late Miocene Cooling, which started at ~7 Ma, and the increased influence of the cooler and more productive Southern Ocean waters, the calcareous nannofossil assemblage evolved into a community characterised by relatively high-nutrient and cold-water taxa (e.g., Coccolithus pelagicus, Calcidiscus leptoporus). By 10.67 Ma, we recorded a reversion in the nannoplankton assemblage to species typical of low-nutrient and warm-water conditions that lasted until 9.88 Ma. The comparison with available eNd(t) records for Site 752 and 707 (located in the equatorial Indian Ocean) revealed that this change in the assemblage composition responded to a strengthening of the Pacific Ocean water influx occurring at this time. High-nutrient and cold-water conditions were reestablished after 9.88 Ma, lasting until the end of the studied record at ~7.34 Ma. Our evaluation of the primary producer community from a multi-proxy-based perspective revealed a progressive evolution of the surface ocean conditions in the southeastern Indian Ocean region across the Middle to Late Miocene for the first time. Furthermore, the strong correlation with existing proxy data for global climate records suggests that large-scale climate events are the main factors driving the changes in the primary producer community and surface ocean conditions at the Broken Ridge during the Middle to Late Miocene. However, certain regional processes (e.g., strengthening of the Pacific Ocean influx) may also occasionally influence surface ocean conditions. Moreover, this multi-proxy approach allowed us to better understand the Indian Ocean–Southern Ocean interaction, and more specifically, the nutrient transport efficiency between these two ocean basins during a climate change scenario. Specifically, our multi-proxy-based dataset revealed that the Antarctic divergence region experienced a northward migration after the MCO, leading to a deep reorganisation of nutrient transport across the surface southeastern Indian Ocean.

Understanding how the Earth’s system behaves under climate forcing conditions is critical for predicting how future climate change scenarios may affect the planet. In this regard, the Miocene, with an atmospheric temperature ~4 °C higher than modern and a near-modern ocean configuration, stands out as a potential analogue for future climate projections. Our current understanding of the Miocene derives principally from the Atlantic and Pacific Oceans, whereas the Indian Ocean remains understudied. Nevertheless, different studies performed in the equatorial Indian Ocean have revealed that the multiple climate shifts that occurred during the Miocene modified both the atmospheric and oceanic processes in this basin (e.g., changes in westerlies position, nutrient flux and productivity). In the present study, we investigate how changes in the climate conditions affected the surface ocean system at Ocean Drilling Program (ODP) Site 752, located in the southeastern Indian Ocean, across the Middle to Late Miocene. For this purpose, we present a new quantitative dataset of calcareous nannofossil assemblages, in conjunction with already existing multi-proxy data. Our results indicate that the warm atmospheric conditions reached during the Miocene Climatic Optimum (MCO), starting at ~16.9 Ma, caused an intensification of the seasonal signal at ODP Site 752 that lasted until 15.32 Ma. After this period, we detected a shift in the calcareous nannofossil assemblage towards species characteristic of low-nutrient and warm-water conditions (e.g., Reticulofenestra pseudoumbilicus, Reticulofenestra haqii). Nevertheless, with the progression towards the Late Miocene Cooling, which started at ~7 Ma, and the increased influence of the cooler and more productive Southern Ocean waters, the calcareous nannofossil assemblage evolved into a community characterised by relatively high-nutrient and cold-water taxa (e.g., Coccolithus pelagicus, Calcidiscus leptoporus). By 10.67 Ma, we recorded a reversion in the nannoplankton assemblage to species typical of low-nutrient and warm-water conditions that lasted until 9.88 Ma. The comparison with available eNd(t) records for Site 752 and 707 (located in the equatorial Indian Ocean) revealed that this change in the assemblage composition responded to a strengthening of the Pacific Ocean water influx occurring at this time. High-nutrient and cold-water conditions were reestablished after 9.88 Ma, lasting until the end of the studied record at ~7.34 Ma. Our evaluation of the primary producer community from a multi-proxy-based perspective revealed a progressive evolution of the surface ocean conditions in the southeastern Indian Ocean region across the Middle to Late Miocene for the first time. Furthermore, the strong correlation with existing proxy data for global climate records suggests that large-scale climate events are the main factors driving the changes in the primary producer community and surface ocean conditions at the Broken Ridge during the Middle to Late Miocene. However, certain regional processes (e.g., strengthening of the Pacific Ocean influx) may also occasionally influence surface ocean conditions. Moreover, this multi-proxy approach allowed us to better understand the Indian Ocean–Southern Ocean interaction, and more specifically, the nutrient transport efficiency between these two ocean basins during a climate change scenario. Specifically, our multi-proxy-based dataset revealed that the Antarctic divergence region experienced a northward migration after the MCO, leading to a deep reorganisation of nutrient transport across the surface southeastern Indian Ocean.

The mid and late Pleistocene are marked by large-amplitude fluctuations in global ice volume and pronounced climatic variability. Around ~1 Ma, Earth’s climate system underwent a fundamental reorganization, as glacial–interglacial variability shifted from predominantly 41-kyr cycles to higher-amplitude, quasi-100-kyr oscillations. This transition was accompanied by enhanced atmospheric CO2 drawdown during glacial periods. However, how the global carbon cycle adjusted to this shift, and which reservoirs account for the lowered glacial atmospheric CO2 concentrations, remains not fully quantitatively constrained. In this context, marine carbon burial, particularly on continental shelves, represents a potentially important yet underexplored long-term sink for atmospheric CO2.Here, we quantify variability in organic and carbonate carbon burial on the West Australian shelf and evaluate its potential contribution to Pleistocene atmospheric CO2 drawdown. We measured δ¹³C and calculated relative burial fractions and mass accumulation rates for organic and carbonate carbon in sediments recovered from IODP Expedition 356 Site U1460 (27°22′S, 112°55′E), spanning the last ~210 kyr (MIS 7–MIS 1). The site was drilled at ~214 m water depth in the northern Perth Basin and is situated in a dynamic oceanographic setting influenced by the interaction between the warm, oligotrophic Leeuwin Current (LC) and the cooler, nutrient-rich West Australian Current (WAC).Our results reveal two pronounced maxima in organic carbon burial relative to carbonate during glacial MIS 6 (~168 ka) and MIS 2 (~26 ka), as well as a more moderate increase at ~109 ka across the MIS 5a–d to MIS 5e transition. These patterns are consistent with previous suggestions of enhanced shelf organic carbon burial during glacial periods (Auer et al., 2021). Variations in organic-to-carbonate burial ratios are paced by eccentricity-modulated glacial–interglacial sea-level changes and Milankovic-driven shifts in seasonality, both of which influence the strength of the LC and its interaction with the WAC. High sea level and enhanced seasonality strengthen the LC, restricting nutrient supply to the West Australian shelf. Conversely, low sea level and reduced seasonality weaken the LC, allowing the nutrient-rich WAC to dominate, thereby enhancing primary productivity and organic carbon burial.Finally, we use organic carbon mass accumulation rates to place first-order constraints on the potential for carbon storage on the West Australian shelf during Late Pleistocene glacials. Although organic carbon burial increased during glacial intervals, limited accommodation space on the shelf likely restricted total organic carbon accumulation, preventing it from exerting a major influence on global glacial–interglacial atmospheric CO₂ variability.

The Middle to Late Miocene constitutes a critical time interval on a global scale. The continental reorganization that occurred during this time caused the establishment of a near-modern monsoonal wind system in the Indian Ocean (IO). Furthermore, this period is characterised by the succession of climatic scenarios linked to the Middle Miocene Climatic Transition (MMCT) and the subsequent northward shift of the Westerlies region during the Late Miocene. How these processes affected and interactedi with the surface ocean dynamics in the southern IO remains poorly understood. In this regard, Ocean Drilling Program (ODP) Site 752, located on the west flank of Broken Ridge (30° 53.475ˈS/93° 34.652ˈE), constitutes a key location to investigate how the aforementioned processes interacted with the surface current in the eastern sector of the southern IO across the Middle to Late Miocene.Changes in the nannofossil assemblage between 7.31 and 16.06 Ma at Site 752 were evaluated to ascertain variations in the surface ocean conditions. A total of 122 samples (temporal resolution of ~60 kyr) were analysed for this purpose. The clustering ordination method UPGMA (Bray-Curtis) revealed a total of 5 clusters (Cluster 1-5). Cluster 5 was additionally divided into two sub-clusters (Cluster 5a-5b). The oceanographic conditions were inferred based on the abundance of the main nannofossil species constituting the clusters: Reticulofenestra minuta, Calcidiscus leptoporus, Coccolithus pelagicus, Reticulofenestra haqii, Reticulofenestra producta, Reticulofenestra pseudoumbilicus, and Reticulofenestra perplexa. Subsequently, the assemblage data were compared with a set of global climatic and geochemical data to ascertain the effect of global processes on the regional oceanographic configuration across the Middle to Late Miocene.Total organic carbon (TOC) and Total Inorganic Carbon (TIC) were measured to ascertain variation in the carbon flux to the ocean floor. Additionally, bulk, organic, and benthic foraminiferal δ13C analyses were performed in order to track productivity changes and variations in the nutrient cycle during the studied time interval in the southern IO and compared with the observed variations in the nannofossil assemblage. Benthic δ13C was measured on two foraminifera species (Lobatula wuellerstorfi and Cibicidoides mundulus).Our data indicate that the surface water of the southern IO was characterised by low nutrient availability and high temperature conditions during the Middle Miocene. After the MMCT, the surface ocean experienced an increase in nutrient availability, which was concomitant with a decrease in δ18O. Maximum surface ocean nutrient conditions were recorded after ~9.9 Ma, coeval with the establishment of the Late Miocene Cooling. A comparison between the nannofossil assemblage data at Site 752 and eNd records available in the literature confirmed the hypothesis that warm water input from the Pacific Ocean into the southern IO increased between ~10.7 – 9.9 Ma. Furthermore, the comparison of the assemblage data against δ13C, TOC, and TIC measured at ODP Site 752 allowed us to disentangle the local processes driving changes in the IO surface water conditions.

The Miocene Climatic Optimum (MCO) represents a climate period characterized by lower ice volumes and temperatures that were 3-4°C warmer than today. Indian Ocean Sub-Antarctic Mode Water (SAMW) is primarily formed south of 30°S and is the main return path for deep waters to the surface, migrating and intermixing northwards at Intermediate Water (IW) depths. The modern SAMW transports nutrients into the lower latitudes, strongly impacting mid- and low latitude productivity. During warmer climates, decreasing sea ice may increase nutrient trapping in the Southern Ocean, reducing the nutrient flux through SAMW into the lower latitudes. To better understand trajectories of nutrient fluxes in future climate change scenarios studies in past warm climate analogues of the near future – such as the MCO – are necessary. Thus, we use Ocean Drilling Project (ODP) Site 752, located on Broken Ridge in the southeastern Indian Ocean at a water depth of 1086.3 m, as a key location for understanding changes in IW conditions. This study aims to reconstruct paleoenvironmental conditions and bottom-water oxygenation at ODP Site 752 during the Middle to Late Miocene (15-8 Ma) using benthic foraminifera assemblages as a proxy for bottom-water-oxygenation and the enhanced Benthic Foraminifera Oxygen Index (eBFOI) for calculating dissolved oxygen content. We combine these assemblage data with Mg/Ca ratios of Cibicidoides wuellerstorfi and Cibicidoides mundulus as a proxy for bottom water temperatures (BWT). For reconstructing sea surface temperatures (SST), and temperatures from the open ocean thermocline, the Mg/Ca data were additionally gathered on the foraminifera species Globigerina bulloides (SST) and Globorotalia menardii (thermocline). We aim to analyze temperature variability through the water column to investigate influxes from cooler water bodies by increasing SAMW intensity and compare our new temperature data with our benthic foraminiferal assemblages. Therefore, we provide novel insights into Late Miocene IW circulation changes and deep water mass variation with the progressive northward shift of the Subantarctic Tropical Front (SAF).We present a high-resolution record of benthic foraminifera, tracing paleoenvironmental changes in deep water masses in addition to IW variation in the southeastern Indian Ocean. After the MCO, benthic foraminifera assemblages, and respectively the eBFOI indicate a relatively high oxic environment. Starting around 11 Ma, we first detect an increase of dysoxic conditions and deep infaunal foraminifera, e.g. the genus Bolivina spp., with minimal variation in the dissolved oxygen content of the bottom water. Such an assemblage shift is contemporary with increased current winnowing following the northward migration of the SAF. Furthermore, the higher abundance of epiphytic species Cibicidoides wuellerstorfi and Lobatula lobatula, and also Vulvulina pennatula as an elevated epifauna, support an increase in bottom current energy at Broken Ridge from 15 to 11 Ma. Combined, our assemblages and Mg/Ca paleotemperature data suggest that the strengthening of the SAMW and Antarctic Intermediate Water formation in the Late Miocene, since about 11 Ma, resulted in notable changes in bottom water conditions at Broken Ridge, including the increase of current winnowing.

The Middle to Late Miocene represents an important time interval on a global scale. Due to continental reorganisation in the Indian Ocean (IO) a near-modern monsoonal wind system was established, a series of climatic changes linked to the Middle Miocene Climatic Transition occurred and the subsequent shift of the region dominated by the Westerlies to the north took place during the Late Miocene. However, how these processes and forcing mechanisms interact and affect the surface ocean dynamics in the southern subtropical IO is poorly understood. In this regard, Ocean Drilling Program (ODP) Site 752, located on the west flank of Broken Ridge (30° 53.475ˈS/93° 34.652ˈE), represents a key location to study how the above-mentioned processes may have affected the surface currents in the eastern sector of the subtropical IO during the Middle to Late Miocene.In order to ascertain changes in the surface ocean conditions and their connection to surface currents dynamics between 7.31 and 16.06 Ma, we evaluated the overall changes in the calcareous nannofossil assemblage at Site 752. For this purpose, we performed a quantitative study on 122 calcareous nannofossil samples (with a temporal resolution of ~60 kyr) and performed statistical analyses to observe variations in the assemblage composition. The UPGMA (Bray-Curtis) clustering ordination analyses revealed a total of 5 clusters (Cluster 1-5), defined at a cut-off distance of ~0.76 and a cophenetic correlation coefficient of 0.75. Additionally, Cluster 5 was divided into two sub-clusters (Cluster 5a-5b), at a cut-off distance of ~0.77.Cluster 1 indicates high nutrient availability due to the abundance of Reticulofenestra minuta. Cluster 2 also indicates high nutrient supply in the region, as per the high abundance of R. minuta, differing from Cluster 1 by the presence of Calcidiscus leptoporus and Coccolithus pelagicus, both indicative of cold surface waters with a deep mixed layer. Cluster 3 is characterised by the concomitant presence of species typical of warm/cold stratified/mixed regions, such as Discoaster spp., C. pelagicus and R. pseudoumbilicus. Cluster 4 is dominated by Reticulofenestra haqii and Reticulofenestra producta, which thrive in warm and oligo/mesotrophic conditions. Reticulofenestra producta is also abundant in Cluster 5a. However, the high abundances of Reticulofenestra perplexa and R. pseudoumbilicus indicate more moderate nutrient conditions with relatively cold surface waters compared to Clusters 1 to 4. Lastly, Cluster 5b is characterised by an increase in the abundance of R. pseudoumbilicus and the common presence of R. haqii, indicating warmer surface water conditions compared with Cluster 5a.Temporal progression from Cluster 4 to Cluster 2 over our study interval reflects a distinct shift to higher nutrient palaeoceanographic conditions at the Broken Ridge between 15–8 Ma. This change in surface water nutrient availability can be linked to an invigoration of the Antarctic Circumpolar Current and the Southern Indian Ocean Current at ODP Site 752. These shifts indicate the impact of the Middle to Late Miocene northward migration of the Westerlies (from 40 to 30º S) on mid-latitude paleoceanographic conditions and confirm the proposed shift in global nutrient cycling around 11 Ma ago.