Response of the Pacific inter-tropical convergence zone to global cooling and initiation of Antarctic glaciation across the Eocene Oligocene Transition

Approximately 34 million years ago across the Eocene–Oligocene transition (EOT), Earth’s climate tipped from a largely unglaciated state into one that sustained large ice sheets on Antarctica. Antarctic glaciation is attributed to a threshold response to slow decline in atmospheric CO2 but our understanding of the feedback processes triggered and of climate change on the other contents is limited. Here we present new geochemical records of terrigenous dust accumulating on the sea floor across the EOT from a site in the central equatorial Pacific. We report a change in dust chemistry from an Asian affinity to a Central-South American provenance that occurs geologically synchronously with the initiation of stepwise global cooling, glaciation of Antarctica and aridification on the northern continents. We infer that the inter-tropical convergence zone of intense precipitation extended to our site during late Eocene, at least four degrees latitude further south than today, but that it migrated northwards in step with global cooling and initiation of Antarctic glaciation. Our findings point to an atmospheric teleconnection between extratropical cooling and rainfall climate in the tropics and the mid-latitude belt of the westerlies operating across the most pivotal transition in climate state of the Cenozoic Era.<br/

Response of the Central Pacific Intertropical Convergence Zone to Northern Hemisphere Cooling During the Last Glacial Maximum and Heinrich Stadial 1

Abstract The latitudinal position of the Intertropical Convergence Zone (ITCZ) reflects the energy imbalance between the hemispheres. Southward displacements of the ITCZ during the Last Glacial Maximum (LGM; 19–26.5 ka) and Heinrich Stadial 1 (HS1; 14.6–17.5 ka), are widely accepted, but their magnitude is controversial. Geochemistry of detrital fractions in down‐core sediments collected from 6°N to equator along the 131.5°W transect reveal a distinct shift in εNd, La/Yb, and La–Sc–Th composition from predominantly northern hemisphere‐sourced to mixed northern and southern hemisphere‐sourced signal at 3°N–4°N during the LGM and 3°N–6°N during HS1. These contrasting provenance signals point to the past ITCZ functioning as a dust barrier. Given that a comparable geochemical demarcation currently occurs at 6°N–7°N, our data suggest that the ITCZ migrated southward by ∼3° during the LGM and ∼1°–3° during HS1 relative to its modern position in the central Pacific

Geochemistry and age data of the down-core sediments collected along 131.5°W transect at the central equatorial Pacific

&lt;p&gt;This dataset includes geochemical composition of inorganic silicate fractions separated from down-core sediments from the central Pacific, with relevant sampling information and radiocarbon and stable oxygen isotope data underlying the age model. The aim of the study is to track position of the Intertropical Convergence Zone during the Last Glacial Maximum and Heinrich Stadial 1 based on the latitudinal changes in hemispheric dust provenance. 7 sediment cores were collected along a 131.5°W transect from the equator to 6°N at ~1º intervals using a multiple corer and a piston corer on the R/V Onnuri during KODOS03-03 cruise (2003.07.03-2003.08.01; Chief Scientist: Woong-Seo Kim) and KODOS05-01 cruise (2005.07.17-2005.08.15; Chief Scientist: Woong-Seo Kim). Subsamples were taken at 1 cm intervals from the split cores, and planktic foraminifera was picked from one to five subsamples per each core for radiocarbon dating. Radiocarbon ages were obtained by AMS, and were calibrated to calender years before present. For one sediment core (MC5111), oxygen isotope ratios (δ18O) of planktic foraminifer, P. obliquiloculata (355–425 μm, ~10 specimens) were measured to supplement radiocarbon ages using IRMS. The inorganic silicate fractions were isolated from bulk sediments by sequential dissolution with 25% acetic acid, hot sodium citrate-sodium dithionite solution buffered with sodium bicarbonate, and hot sodium hydroxide solution. The elemental composition of the inorganic silicate fraction was determined using a quadrupole ICP-MS following conventional acid digestion. 143Nd/144Nd ratios were determined via multi-collector thermal ionization mass spectrometer using standard cation exchange techniques.&lt;/p&gt

A skeletal Sr/Ca record preserved inDipsastraea(Favia)speciosaand implications for coral Sr/Ca thermometry in mid-latitude regions

[1] A core (900 mm long) of the scleractinian coral Dipsastraea (Favia) speciosa was collected from Iki Island (∼33°48′N), Japan, one of the highest latitude coral reefs known to exist at present, where winter monthly mean sea surface temperature (SST) drops to 13°C. The Sr/Ca profile was constructed using a bulk sampling method for the uppermost 280 mm interval of the core, which grew between 1966 and 2007, to test whether it could act as a suitable proxy for SST in a harsh environmental setting where reef-building coral do not usually survive. The Sr/Ca-SST relationship derived from the annual Sr/Ca and SST extremes predicted the observed monthly averaged summer SST extremes within an error range of ±1.1°C (1 s.d., n = 40). The obtained Sr/Ca-SST calibration was also found to be valid for subtropical Dipsastraea (Favia) corals, proving its broad applicability. However, low-amplitude winter peaks were observed in the slow-growing intervals, which we confirmed (using individual spot analysis along a continuous growth line) result from the mixing of theca grown at different times. Our bulk sampling approach, across multiple growth lines in the skeleton of D. (F.) speciosa, led to the mixing of asynchronous skeletal part. At the study site, D. (F.) speciosa grows continuously, even during the cold season, suggesting that the skeletal Sr/Ca obtained from specimens of D. (F.) speciosa can be used as an SST proxy in the northwest Pacific marginal seas

Rare Earth Elements and Other Critical Metals in Deep Seabed Mineral Deposits: Composition and Implications for Resource Potential

The critical metal contents of four types of seabed mineral resources, including a deep-sea sediment deposit, are evaluated as potential rare earth element (REE) resources. The deep-sea resources have relatively low total rare earth oxide (TREO) contents, a narrow range of TREO grades (0.049&#8315;0.185%), and show characteristics that are consistent with those of land-based ion adsorption REE deposits. The relative REO distributions of the deep-seabed resources are also consistent with those of ion adsorption REE deposits on land. REEs that are not part of a crystal lattice of host minerals within deep-sea mineral deposits are favorable for mining, as there is no requirement for crushing and/or pulverizing during ore processing. Furthermore, low concentrations of Th and U reduce the risk of adverse environmental impacts. Despite the low TREO grades of the deep-seabed mineral deposits, a significant TREO yield from polymetallic nodules and REE-bearing deep-sea sediments from the Korean tenements has been estimated (1 Mt and 8 Mt, respectively). Compared with land-based REE deposits, deep-sea mineral deposits can be considered as low-grade mineral deposits with a large tonnage. The REEs and critical metals from deep-sea mineral deposits are important by-products and co-products of the main commodities (e.g., Co and Ni), and may increase the economic feasibility of their extraction

Geochemical composition of inorganic silicate fraction of surface sediment samples collected along a 131.5°W transect in the central Pacific

This dataset includes neodymium isotope ratios and La, Yb, Sc, and Th concentrations of inorganic silicate fractions of surface sediments from the central Pacific, with relevant sampling information. The aim of the study is to identify latitudinal changes in hemispheric dust provenance. 16 sediment cores were collected along a 131.5°W transect from the equator to 16°N at ~1º intervals using a multiple corer and a piston corer on the R/V Onnuri during KODOS03-03 cruise (2003.07.03-2003.08.01; Chief Scientist: Woong-Seo Kim) and KODOS05-01 cruise (2005.07.17-2005.08.15; Chief Scientist: Woong-Seo Kim). Subsamples were taken at 1 cm intervals from the split cores, and those obtained within the top 10 cm of the cores (usually within the top 3 cm) were used to extract the inorganic silicate fraction. The inorganic silicate fractions of bulk sediments were isolated by sequential dissolution with 25% acetic acid, hot sodium citrate-sodium dithionite solution buffered with sodium bicarbonate, and hot sodium hydroxide solution. The elemental composition of the inorganic silicate fraction was determined using a quadrupole ICP-MS following conventional acid digestion. 143Nd/144Nd ratios were determined via multi-collector thermal ionization mass spectrometer using standard cation exchange techniques

Climatic evolution of the central equatorial Pacific since the Last Glacial Maximum

This paper investigates paleoceanographic changes at a central equatorial Pacific site (6 degrees 40N, 177 degrees 28W) since the last glacial maximum using planktic foraminifera assemblages, together with the oxygen isotope (O-18) and Mg/Ca compositions of three species (Globigerinoides sacculifer, Pulleniatina obliquiloculata, and Globorotalia tumida) that dwell in the mixed layer, upper thermocline, and lower thermocline, respectively. While the Mg/Ca-derived temperatures of the mixed layer and lower thermocline varied within a narrow range from 18 ka onward, the upper thermocline temperature increased by as much as 3 degrees C during the last deglaciation (18-12 ka) with a simultaneous decrease of O-18. These changes are best explained by an enhanced mixing of the upper ocean and a reduced habitat depth separation between P. obliquiloculata and G. sacculifer during the 18-12 ka interval. The planktic foraminifera assemblage during the same period resembles modern composition at subtropical central Pacific sites that are strongly influenced by the northeasterly Trades and North Equatorial Current (NEC). We suggest that the study site, presently under the control of the Intertropical Convergence Zone (ITCZ)-North Equatorial Countercurrent, had been influenced by the northeasterly Trades and NEC during the 18-12 ka interval. This interpretation is consistent with previous documentation of a more southerly location of the ITCZ during two Northern Hemisphere cooling events; the Heinrich Stadial 1 and the Younger Dryas, and implies that the mean annual position of the ITCZ was located south of the study site, by at least 2 degrees of latitude

Characterization of Fines Produced by Degradation of Polymetallic Nodules from the Clarion–Clipperton Zone

The discharge of fluid–particle mixture tailings can cause serious disturbance to the marine environment in deep-sea mining of polymetallic nodules. Unrecovered nodule fines are one of the key components of the tailings, but little information has been gained on their properties. Here, we report major, trace, and rare earth element compositions of &lt;63 μm particles produced by the experimental degradation of two types of polymetallic nodules from the Clarion–Clipperton Zone. Compared to the bulk nodules, the fines produced are enriched in Al, K, and Fe and depleted in Mn, Co, Ni, As, Mo, and Cd. The deviation from the bulk composition of original nodules is particularly pronounced in the finer fraction of particles. With X-ray diffraction patterns showing a general increase in silicate and aluminosilicates in the fines, the observed trends indicate a significant contribution of sediment particles released from the pores and cracks of nodules. Not only the amount but also the composition of nodule fines is expected to significantly differ depending on the minimum recovery size of particles at the mining vessel