Description: The Line Islands Ridge (LIR), located south of the Hawaiian Islands between 7°N and 1°S, is one of the few large central Pacific regions shallower than the regional carbonate compensation depth. Thick sequences of carbonate sediments have accumulated around the LIR despite it being located in the sediment-starved central tropical Pacific. The LIR is an important source of carbonates to the surrounding region and deposition around the LIR has expanded the equatorial Pacific carbonate sediment tongue by about 5% of its total area. Furthermore, sediments on the ridge are potentially important paleoceanographic archives. A recent survey at the crest of the LIR finds evidence for high current activity, significant erosion, but overall net sediment deposition. Currents are strong enough to form sediment waves and lee drifts in the Palmyra Basin, at the northern terminus of the LIR. Sediments along the LIR are pelagic foraminiferal sands that are easily eroded and flow out into the surrounding abyssal plain in active submarine channel systems. As channels migrate, pelagic sediments fill in the abandoned channel arms. Despite significant sediment losses from the top of the ridge, 1.3 km of sediment has accumulated in the upper Palmyra Basin over basement formed 68 to 85 million years ago (Ma). Late Neogene erosion may be more extensive than earlier erosion cycles, in response to reduced sediment production as the Palmyra Basin exited the high productivity equatorial latitudes. Sediments with good stratigraphic order needed for paleoceanographic study are limited in this dynamic sedimentary environment, but can be found with proper survey.

Description: The late Miocene-early Pliocene was a time of global cooling and the development of modern meridional thermal gradients. Equatorial Pacific sea surface conditions potentially played an important role in this global climate transition, but their evolution is poorly understood. Here, we present the first continuous late Miocene-early Pliocene (8.0-4.4 Ma) planktic foraminiferal stable isotope records from eastern equatorial Pacific Integrated Ocean Drilling Program Site U1338, with a new astrochronology spanning 8.0-3.5 Ma. Mg/Ca analyses on surface dwelling foraminifera Trilobatus sacculifer from carefully selected samples suggest mean sea-surface-temperatures (SSTs) are ~27.8±1.1°C (1 Sigma) between 6.4-5.5 Ma. The planktic foraminiferal d18O record implies a 2°C cooling between 7.2-6.1 Ma and an up to 3°C warming between 6.1-4.4 Ma, consistent with observed tropical alkenone paleo-SSTs. Diverging fine-fraction-to-foraminiferal d13C gradients likely suggest increased upwelling from 7.1-6.0 and 5.8-4.6 Ma, concurrent with the globally recognized late Miocene Biogenic Bloom. This study shows that both warm and asymmetric mean states occurred in the equatorial Pacific during the late Miocene-early Pliocene. Between 8.0-6.5 and 5.2-4.4 Ma, low east-west d18O and SST gradients and generally warm conditions prevailed. However, an asymmetric mean climate state developed between 6.5-5.7 Ma, with larger east-west d18O and SST gradients and eastern equatorial Pacific cooling. The asymmetric mean state suggests stronger trade winds developed, driven by increased meridional thermal gradients associated with global cooling and declining atmospheric pCO2 concentrations. These oscillations in equatorial Pacific mean state are reinforced by Antarctic cryosphere expansion and related changes in oceanic gateways (e.g., Central American Seaway/Indonesian Throughflow restriction).

Description: The Miocene Climatic Optimum (MCO; ~16.9 to 14.7 Ma) provides an outstanding opportunity to investigate climate-carbon cycle dynamics during a geologically recent interval of global warmth. We present benthic stable oxygen (d18O) and carbon (d13C) isotope records (5-12 kyr time resolution) spanning the late early to middle Miocene interval (18 to 13 Ma) at Integrated Ocean Drilling Program (IODP) Site U1335 (eastern equatorial Pacific Ocean). The U1335 stable isotope series track the onset and development of the MCO as well as the transitional climatic phase culminating with global cooling and expansion of the East Antarctic ice-sheet at ~13.8 Ma. We integrate these new data with published stable isotope, geomagnetic polarity and X-ray fluorescence (XRF) scanner-derived carbonate records from IODP Sites U1335, U1336, U1337 and U1338 on a consistent, astronomically-tuned timescale. Benthic isotope and XRF scanner-derived CaCO3 records depict prominent 100 kyr variability with 400 kyr cyclicity additionally imprinted on d13C and CaCO3 records, pointing to a tight coupling between the marine carbon cycle and climate variations. Our inter-site comparison further indicates that the lysocline behaved in highly dynamic manner throughout the MCO, with 〉75% carbonate loss occurring at paleo-depths ranging from ~3.4 to ~4 km in the eastern equatorial Pacific Ocean. Carbonate dissolution maxima coincide with warm phases (d18O minima) and d13C decreases, implying that climate-carbon cycle feedbacks fundamentally differed from the late Pleistocene glacial-interglacial pattern, where dissolution maxima correspond to d13C maxima and d18O minima. Carbonate dissolution cycles during the MCO were, thus, more similar to Paleogene hyperthermal patterns.

Description: Obtaining geochemical profiles using X-ray fluorescent (XRF) techniques has become a standard procedure in many sediment core studies. The resulting datasets are not only important tools for palaeoclimatic and palaeoceanographic reconstructions, but also for stratigraphic correlation. The International Ocean Discovery Program (IODP) has therefore recently introduced shipboard application of a handheld XRF device, making geochemical data directly available to the science party. In all XRF scanning techniques, the physical properties of wet core halves cause substantial analytical deviations. In order to obtain estimates of element concentrations (e.g. for quantitative analyses of fluxes or mass-balance calculations), a calibration of the scanning data is required. We test whether results from the handheld XRF analysis on discrete samples are suitable for calibrating scanning data. Log-ratios with Ca as a common denominator were calculated. The comparison between the handheld device and conventional measurements show that the latter provide high-quality data describing Al, Si, K, Ca, Ti, Mn, Fe, Zn, Rb and Sr content (R2 compared with conventional measurements: ln(Al/Ca) = 0.99, ln(Si/Ca) = 0.98, ln(K/Ca) = 0.99, ln(Ti/Ca) = 0.99, ln(Mn/Ca) = 0.99, ln(Fe/Ca) = 0.99, ln(Zn/Ca) = 0.99 and ln(Sr/Ca) = 0.99). Our results imply that discrete measurements using the shipboard handheld analyser are suitable for the calibration of XRF scanning data. Our test was performed on downcore sediments from IODP Expedition 355 that display a wide variety of lithologies of both terrestrial and marine origin. The implication is that our findings are valid on a general scale and that shipboard handheld XRF analysis on discrete samples should be used for calibrating XRF scanning data.