Paleoceanography最新文献

{"title":"Influence of ocean tides on the general ocean circulation in the early Eocene","authors":"T. Weber, Maik Thomas","doi":"10.1002/2016PA002997","DOIUrl":"https://doi.org/10.1002/2016PA002997","url":null,"abstract":"The early Eocene (∼56-50 million years ago) was characterized by higher surface temperatures and a reduced meridional temperature gradient, compared to present-day conditions. The origin of the decreased meridional temperature gradient is still subject to discussion and might be linked to tides. Tidal mixing could have enhanced the meridional heat transport and thereby decreased the meridional temperature gradient. We test this hypothesis by simultaneously modelling tidal dynamics and the general ocean circulation for the early Eocene in a new coupled atmosphere-ocean model setup. We find an interaction between tidal currents and the ocean general circulation that increases horizontal velocities in 25% of the deep ocean to more than 400% of its original value. The global meridional overturning circulation (GMOC) is strengthened thereby locally by 60-100%. However, the oceanic meridional heat transport is only increased by a maximum of 0.1PW (8%) and a mean of less than 0.018PW (5.1%), thus not decreasing the meridional temperature gradient considerably.","PeriodicalId":19882,"journal":{"name":"Paleoceanography","volume":"32 1","pages":"553-570"},"PeriodicalIF":0.0,"publicationDate":"2017-06-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://sci-hub-pdf.com/10.1002/2016PA002997","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"42803684","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"New evidence for Kuroshio inflow and deepwater circulation in the Okinawa Trough, East China Sea: Sedimentary mercury variations over the last 20 kyr","authors":"D. Lim, Jihun Kim, Zhaokai Xu, K. Jeong, H. Jung","doi":"10.1002/2017PA003116","DOIUrl":"https://doi.org/10.1002/2017PA003116","url":null,"abstract":"The evolution of the Kuroshio Current (KC) in the Okinawa Trough (OT) has long been of paleoceanographic interest and has been the focus of many investigations because of its large impacts on both the ocean environment and the climate in East Asia. Here, we present a new high-resolution mercury (Hg) record from the OT sediments that provides robust evidence for the glacial-interglacial variabilities of KC inflow. The Hg levels are anomalously high in the Holocene deposits, which feature a large and abrupt Hg increase at ~9.6 ka and a significant drop at 4.5–3.2 ka. Our observations show that most Hg was derived from seafloor hydrothermal plumes via active lateral transportation. Thus, the generally high Hg levels since ~9.6 ka are associated with enhanced basin-wide deep-water circulation triggered by the KC inflow. This driving mechanism for the deposition and widespread of Hg is also evidenced by an abrupt drop in Hg levels during the late Holocene neoglacial cold period (~5–3 ka) when the KC inflow was temporarily interrupted and deep-water circulation was consequently weak or even absent in the OT. The changes in sedimentary Hg appear to be synchronous with those in other geochemical proxies that suggest that bottom water conditions switched from anoxic to oxic due to increased upwelling from the bottom in tandem with the strengthening KC and reduced freshwater effect since ~9.6 ka. This study shows that the hydrothermal Hg is a sensitive and independent tool for the reconstruction of palaeo-dynamics of KC in the OT.","PeriodicalId":19882,"journal":{"name":"Paleoceanography","volume":"32 1","pages":"571-579"},"PeriodicalIF":0.0,"publicationDate":"2017-06-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://sci-hub-pdf.com/10.1002/2017PA003116","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"47216797","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Closing an early Miocene astronomical gap with Southern Ocean δ18O and δ13C records: Implications for sea level change","authors":"K. Miller, Ronidell Baluyot, J. Wright, R. Kopp, J. Browning","doi":"10.1002/2016PA003074","DOIUrl":"https://doi.org/10.1002/2016PA003074","url":null,"abstract":"We present orbital-scale resolution (~10-kyr) benthic foraminiferal δ18O and δ13C records from the Kerguelen Plateau (Ocean Drilling Program [ODP] Sites 751 and 747) from 14.5-20.0 Ma spanning the Miocene climate optimum (MCO; 15-17 Ma). Our records fill a critical gap from ~17-18 Ma, a time when many other deep-sea records are affected by dissolution. We tested the fidelity of published magneto-biostratigraphic age models for these sites by astronomically tuning to the 405-kyr eccentricity cycle. A comparison of spectral estimates between the untuned and tuned records, as well as coherency with Laskar's (2004) eccentricity solution, revealed quasi-100-kyr cyclicity in δ18O and δ13C. There is only a weak signal associated with the 41-kyr obliquity cycle, likely due to the 10-kyr sampling limiting resolution. The δ18O variations point to persistent 405- and quasi-100-kyr modulations of temperature and sea-level changes through the early to middle Miocene as predicted by astronomical solutions, with changing dominance of the 100- and 41-kyr beat. Comparison of δ18O records with early to middle Miocene sequences from the New Jersey shelf, northeast Australian margin, Bahamas, and Maldives suggests that the dominant sea-level period preserved is the 1.2-Myr obliquity cycle, with sequence boundaries associated with δ18O increases or maxima. On the New Jersey margin, higher order sequences reflect the quasi-100-kyr eccentricity cycles as modulated by 405-kyr cycles. We suggest that “nesting” of stratigraphic cycles is a function of: 1) pervasive (though changing) Milankovitch forcing of global mean sea-level change; and 2) preservation that depends on sufficient sediment supply and accommodation.","PeriodicalId":19882,"journal":{"name":"Paleoceanography","volume":"32 1","pages":"600-621"},"PeriodicalIF":0.0,"publicationDate":"2017-06-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://sci-hub-pdf.com/10.1002/2016PA003074","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"43511037","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Precessional variability of 87 Sr/86 Sr in the late Miocene Sorbas Basin: An interdisciplinary study of drivers of interbasin exchange","authors":"S. Modestou, D. Simon, M. Gutjahr, A. Marzocchi, T. Kouwenhoven, R. Ellam, R. Flecker","doi":"10.1002/2016PA003061","DOIUrl":"https://doi.org/10.1002/2016PA003061","url":null,"abstract":"We present the first subprecessional record of seawater 87Sr/86Sr isotope ratios for a marginal Mediterranean subbasin. The sediments contained in this interval (three precessional cycles between 6.60 and 6.55 Ma) are important because they record conditions during the transition to the Messinian Salinity Crisis (MSC; 5.97 to 5.33 Ma), an event for which many details are still poorly understood. The record, derived from planktic foraminifera of the late Miocene Sorbas Basin (SE Spain), shows brief excursions with precessional cyclicity to 87Sr/86Sr ratios higher than coeval ocean 87Sr/86Sr. The hydrologic conditions required to generate the observed record are investigated using box modeling, constrained using a new paleodepth estimate (150 to 250 m) based on benthic foraminiferal assemblages. The box model results highlight the role of climate-driven interbasin density contrast as a significant driver of, or impediment to, exchange. The results are particularly significant in the context of the MSC, where 87Sr/86Sr excursions have been interpreted purely as a consequence of physical restriction. To replicate the observed temporal patterns of lithological variations and 87Sr/86Sr isotope excursions, the Sorbas Basin “box” must have a mainly positive hydrologic budget, in contrast with the Mediterranean's negative budget during the late Miocene. This result has implications for the assumption of synchronous deposition of specific sedimentary layers (sapropels) between marginal and open Mediterranean settings at subprecessional resolution. A net positive hydrologic budget in marginal Mediterranean subbasins may reconcile observations of freshwater inclusions in gypsum deposits.","PeriodicalId":19882,"journal":{"name":"Paleoceanography","volume":"32 1","pages":"531-552"},"PeriodicalIF":0.0,"publicationDate":"2017-06-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://sci-hub-pdf.com/10.1002/2016PA003061","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"46420235","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Synchronous and proportional deglacial changes in Atlantic meridional overturning and northeast Brazilian precipitation","authors":"S. Mulitza, C. Chiessi, E. Schefuß, J. Lippold, David Wichmann, Benny Antz, A. Mackensen, A. Paul, M. Prange, K. Rehfeld, M. Werner, T. Bickert, N. Frank, H. Kuhnert, J. Lynch‐Stieglitz, R. Portilho-Ramos, A. Sawakuchi, M. Schulz, T. Schwenk, R. Tiedemann, M. Vahlenkamp, Yancheng Zhang","doi":"10.1002/2017PA003084","DOIUrl":"https://doi.org/10.1002/2017PA003084","url":null,"abstract":"Changes in heat transport associated with fluctuations in the strength of the Atlantic meridional overturning circulation (AMOC) are widely considered to affect the position of the Intertropical Convergence Zone (ITCZ), but the temporal immediacy of this teleconnection has to date not been resolved. Based on a high resolution marine sediment sequence over the last deglaciation, we provide evidence for a synchronous and near-linear link between changes in the Atlantic interhemispheric sea surface temperature difference and continental precipitation over northeast Brazil. The tight coupling between AMOC strength, sea surface temperature difference and precipitation changes over northeast Brazil unambiguously points to a rapid and proportional adjustment of the ITCZ location to past changes in the Atlantic meridional heat transport.","PeriodicalId":19882,"journal":{"name":"Paleoceanography","volume":"32 1","pages":"622-633"},"PeriodicalIF":0.0,"publicationDate":"2017-06-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://sci-hub-pdf.com/10.1002/2017PA003084","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"45388528","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Calibration of the carbon isotope composition (δ13C) of benthic foraminifera","authors":"A. Schmittner, H. Bostock, O. Cartapanis, W. Curry, H. Filipsson, E. Galbraith, J. Gottschalk, J. Herguera, B. Hoogakker, S. Jaccard, L. Lisiecki, D. Lund, G. Martínez﹣Méndez, J. Lynch‐Stieglitz, A. Mackensen, E. Michel, A. Mix, D. Oppo, C. Peterson, J. Repschläger, E. Sikes, H. Spero, C. Waelbroeck","doi":"10.1002/2016PA003072","DOIUrl":"https://doi.org/10.1002/2016PA003072","url":null,"abstract":"The carbon isotope composition (δ13C) of seawater provides valuable insight on ocean circulation, air-sea exchange, the biological pump, and the global carbon cycle and is reflected by the δ13C of foraminifera tests. Here more than 1700 δ13C observations of the benthic foraminifera genus Cibicides from late Holocene sediments (δ13CCibnat) are compiled and compared with newly updated estimates of the natural (preindustrial) water column δ13C of dissolved inorganic carbon (δ13CDICnat) as part of the international Ocean Circulation and Carbon Cycling (OC3) project. Using selection criteria based on the spatial distance between samples, we find high correlation between δ13CCibnat and δ13CDICnat, confirming earlier work. Regression analyses indicate significant carbonate ion (−2.6 ± 0.4) × 10−3‰/(μmol kg−1) [CO32−] and pressure (−4.9 ± 1.7) × 10−5‰ m−1 (depth) effects, which we use to propose a new global calibration for predicting δ13CDICnat from δ13CCibnat. This calibration is shown to remove some systematic regional biases and decrease errors compared with the one-to-one relationship (δ13CDICnat = δ13CCibnat). However, these effects and the error reductions are relatively small, which suggests that most conclusions from previous studies using a one-to-one relationship remain robust. The remaining standard error of the regression is generally σ ≅ 0.25‰, with larger values found in the southeast Atlantic and Antarctic (σ ≅ 0.4‰) and for species other than Cibicides wuellerstorfi. Discussion of species effects and possible sources of the remaining errors may aid future attempts to improve the use of the benthic δ13C record.","PeriodicalId":19882,"journal":{"name":"Paleoceanography","volume":"32 1","pages":"512-530"},"PeriodicalIF":0.0,"publicationDate":"2017-06-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://sci-hub-pdf.com/10.1002/2016PA003072","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"48988625","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Mediterranean Outflow Water dynamics during the past ~570 kyr: Regional and global implications","authors":"S. Kaboth, B. Boer, A. Bahr, C. Zeeden, L. Lourens","doi":"10.1002/2016PA003063","DOIUrl":"https://doi.org/10.1002/2016PA003063","url":null,"abstract":"The Gulf of Cadiz constitutes a prime area to study teleconnections between the North Atlantic Ocean and climate change in the Mediterranean realm. In particular, the highly saline Mediterranean Outflow Water (MOW) is an important modulator of the North Atlantic salt budget on intermediate water levels. However, our understanding of its paleoceanographic evolution is poorly constrained due to the lack of high-resolution proxy records that predate the last glacial cycle. Here we present the first continuous and high-resolution (~ 1 kyr) benthic δ18O and δ13C as well as grain size records from Integrated Ocean Drilling Program Site U1386 representing the last ~570 kyr. We find three distinct phases of MOW variability throughout the Late to Middle Pleistocene at Site U1386 associated with prominent shifts in its composition and flow strength. We attribute this long-term variability to changes in water mass sourcing of the MOW. Superimposed on the long-term change in water mass sourcing is the occurrence of distinct and precession paced δ18O enrichment events, which contrast the pattern of global ice volume change as inferred from the global mean δ18O signal (i.e., LR04) but mimics that of the adjacent Mediterranean Sea. We attribute these enrichment events to a profound temperature reduction and salinity increases of the MOW, aligning with similar changes in the Mediterranean source region. These events might further signify ice volume increases as inferred from significant sea level drops recorded in the Red Sea and/or increased influence of North Atlantic intermediate water masses when MOW influence was absent at Site U1386.","PeriodicalId":19882,"journal":{"name":"Paleoceanography","volume":"32 1","pages":"634-647"},"PeriodicalIF":0.0,"publicationDate":"2017-06-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://sci-hub-pdf.com/10.1002/2016PA003063","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"43397601","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Calibration of the B/Ca proxy in the planktic foraminifer Orbulina universa to Paleocene seawater conditions","authors":"L. Haynes, B. Hönisch, K. Dyez, K. Holland, Y. Rosenthal, Carina R. Fish, A. Subhas, J. Rae","doi":"10.1002/2016PA003069","DOIUrl":"https://doi.org/10.1002/2016PA003069","url":null,"abstract":"The B/Ca ratio of planktic foraminiferal calcite, a proxy for the surface ocean carbonate system, displays large negative excursions during the Paleocene-Eocene Thermal Maximum (PETM, 55.9 Ma), consistent with rapid ocean acidification at that time. However, the B/Ca excursion measured at the PETM exceeds a magnitude that modern pH calibrations can explain. Numerous other controls on the proxy have been suggested, including foraminiferal growth rate and the total concentration of dissolved inorganic carbon (DIC). Here we present new calibrations for B/Ca versus the combined effects of pH and DIC in the symbiont-bearing planktic foraminifer Orbulina universa, grown in culture solutions with simulated Paleocene seawater elemental composition (high [Ca], low [Mg], and low total boron concentration ([B]_T). We also investigate the isolated effects of low seawater [B]_T, high [Ca], reduced symbiont photosynthetic activity, and average shell growth rate on O. universa B/Ca in order to further understand the proxy systematics and to determine other possible influences on the PETM records. We find that average shell growth rate does not appear to determine B/Ca in high calcite saturation experiments. In addition, our “Paleocene” calibration shows higher sensitivity than the modern calibration at low [B(OH)_4−]/DIC. Given a large DIC pulse at the PETM, this amplification of the B/Ca response can more fully explain the PETM B/Ca excursion. However, further calibrations with other foraminifer species are needed to determine the range of foraminifer species-specific proxy sensitivities under these conditions for quantitative reconstruction of large carbon cycle perturbations.","PeriodicalId":19882,"journal":{"name":"Paleoceanography","volume":"32 1","pages":"580-599"},"PeriodicalIF":0.0,"publicationDate":"2017-06-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://sci-hub-pdf.com/10.1002/2016PA003069","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"47343504","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Spatiotemporal variability in the δ¹⁸O-salinity relationship of seawater across the tropical Pacific Ocean.","authors":"Jessica L Conroy,&nbsp;Diane M Thompson,&nbsp;Kim M Cobb,&nbsp;David Noone,&nbsp;Solanda Rea,&nbsp;Allegra N LeGrande","doi":"10.1002/2016PA003073","DOIUrl":"https://doi.org/10.1002/2016PA003073","url":null,"abstract":"<p><p>The relationship between salinity and the stable oxygen isotope ratio of seawater (δ¹⁸O_sw) is of utmost importance to the quantitative reconstruction of past changes in salinity from δ¹⁸O values of marine carbonates. This relationship is often considered to be uniform across water masses, but the constancy of the δ¹⁸O_sw-salinity relationship across space and time remains uncertain, as δ¹⁸O_sw responds to varying atmospheric vapor sources and pathways, while salinity does not. Here we present new δ¹⁸O_sw-salinity data from sites spanning the tropical Pacific Ocean. New data from Palau, Papua New Guinea, Kiritimati, and Galápagos show slopes ranging from 0.09 ‰/psu in the Galápagos to 0.32‰/psu in Palau. The slope of the δ¹⁸O_sw-salinity relationship is higher in the western tropical Pacific versus the eastern tropical Pacific in observations and in two isotope-enabled climate models. A comparison of δ¹⁸O_sw-salinity relationships derived from short-term spatial surveys and multi-year time series at Papua New Guinea and Galápagos suggests spatial relationships can be substituted for temporal relationships at these sites, at least within the time period of the investigation. However, the δ¹⁸O_sw-salinity relationship varied temporally at Palau, likely in response to water mass changes associated with interannual El Niño-Southern Oscillation (ENSO) variability, suggesting nonstationarity in this local δ¹⁸O_sw-salinity relationship. Applying local δ¹⁸O_sw-salinity relationships in a coral δ¹⁸O forward model shows that using a constant, basin-wide δ¹⁸O_sw-salinity slope can both overestimate and underestimate the contribution of δ¹⁸O_sw to carbonate δ¹⁸O variance at individual sites in the western tropical Pacific.</p>","PeriodicalId":19882,"journal":{"name":"Paleoceanography","volume":"Volume 32 Iss 5","pages":"484-497"},"PeriodicalIF":0.0,"publicationDate":"2017-05-13","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://sci-hub-pdf.com/10.1002/2016PA003073","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"37611704","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"The Holocene Labrador Current: Changing linkages to atmospheric and oceanographic forcing factors","authors":"H. Rashid, D. Piper, K. Lazar, Kieran McDonald, F. Saint-Ange","doi":"10.1002/2016PA003051","DOIUrl":"https://doi.org/10.1002/2016PA003051","url":null,"abstract":"The role of Labrador Current (LC) in providing freshwater to the North Atlantic and hence modulating the Atlantic meridional overturning circulation (AMOC) has been debated with very few data. This study provides the first data on the relative speed of the LC for the past 9.2 ka using mean size of the sortable silt of sediments as a proxy from a mid-shelf basin in the western Labrador Sea. LC speed progressively intensified from 9.2–5 ka, during which two meltwater events had minor influence. The LC was fastest between 5 ka and 3.1 ka and gradually weakened after 3.1 ka. The mean size of the sortable silt data shows overall co-variations with similar existing data from deep-water areas of the greater North Atlantic, suggesting an overarching link that modulates changes in both the near-surface and deep North Atlantic. A dynamical link between the LC and AMOC vigor is hypothesized in which high meltwater discharge in the Labrador Sea oriented the subpolar gyre (SPG) more North-South (meridional), weakening the SPG, and thus decelerating the upper limb of the AMOC. Conversely, reduction in LC transport during the late Holocene, due to the greater export of sea ice, oriented the SPG more East-West.","PeriodicalId":19882,"journal":{"name":"Paleoceanography","volume":"32 1","pages":"498-510"},"PeriodicalIF":0.0,"publicationDate":"2017-05-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://sci-hub-pdf.com/10.1002/2016PA003051","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"43268624","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}