Paleoceanography

Zooarchaeological Analysis of the Indigenous Fishery at the Huu7ii Big House and Back Terrace, Huu-ay-aht Territory, Southwestern Vancouver Island

by Iain McKechnie

(2012) Zooarchaeological Analysis of the Indigenous Fishery at the Huu7ii Big House and Back Terrace, Huu-ay-aht Territory, Southwestern Vancouver Island. In Huu7ii: Household Archaeology at a Nuu-chah-nulth Village Site in Barkley Sound, by Alan D. McMillan and Denis E. St. Claire. Archaeology Press, Simon Fraser University, Burnaby, BC.

This paper describes how fish overwhelmingly dominates the animal bone assemblage from the examined column sample... more This paper describes how fish overwhelmingly dominates the animal bone assemblage from the examined column sample deposits at the Huu7ii village site, the named ancestral village of the Huu-ay-aht First Nation. Fish represent 99.9% of all identified bone specimens and are present in every examined litre of sediment indicating the importance of fish in the everyday life of site occupants. The bone assemblage is numerically dominated by Pacific herring, which vastly outnumbers the next most abundant fish: anchovy, salmon, hake, greenling, dogfish, and rockfish as well as two-dozen other fish taxa. I conduct a series of descriptive, quantitative, and graphical analyses that seek to interpret resource harvesting practices at the two examined portions of the site: a very large house (17x35m) dating to the late-Holocene (ca. 1,500-400 yr BP) and mid-Holocene midden deposits recovered on a raised beach terrace (ca. 5,000-3,000 yr BP).

Neogene history of the Indo-Pacific Warm Pool, Kuroshio and Leeuwin Currents

by Stephen Gallagher

A record of early to middle Holocene hydrologic variability from the West African Sahel

by Douglas Park 

American Geophysical Union, 2011, abstract #PP41B-1746
Roderick McIntosh, Peter Douglas, Courtney Warren, S. Meyers, Peter Coutros, Douglas Park

The African Humid Period (ca. 14.8 to 5.5 ka) is an interval of wet climates across northwest Africa, with evidence... more The African Humid Period (ca. 14.8 to 5.5 ka) is an interval of wet climates across northwest Africa, with evidence for widespread lake basins and savannah vegetation in areas that are now desert. There are few high-resolution continental records of hydrologic variability during the African humid period however. In particular, it remains uncertain how periods of north Atlantic climate variability were expressed in northwest Africa. We present results from a 5.4 meter sediment core from Lake Fati in northern Mali (16.29° N, 3.71° W), which represents the first lake sediment core from the western Sahel. The Lake Fati core contains a continuous record of lake mud from 10.43 to 4.66 kyr BP. Centimeter scale XRF scanning indicates strong covariation between iron, calcium, manganese and phosphorous abundance due to enrichment of these elements during periods of enhanced deposition of authigenic siderite. Preliminary oxygen isotope measurements indicate that authigenic siderite δ18O values are positively correlated with Fe counts, suggesting that siderite deposition increased during drier periods with greater evaporation of lake waters. These drying events occurred on decadal to centennial time scales, with higher-frequency variability during the early Holocene. Peaks in zirconium and titanium abundance coincide with some of the inferred dry periods, suggesting that deposition of aeolian silt coincided with periods of increased evaporation of lake water. A roughly 30 year interval of sand deposition at ~8.33 kyr BP suggests major drying and activation of aeolian sand deposition. This abrupt climate change could be related to the 8.2 ka event in the North Atlantic; further efforts to refine the sediment core age model will constrain the relationship of this rapid drying to abrupt climate change in the North Atlantic. Aluminum and silicon counts co-vary for much of the lake Fati record, and are related to input of terrigenous sediment, primarily during seasonal flooding of the Niger river. Al and Si exhibit peak abundance at approximately 9.9 ka followed by a long-term decline, suggesting a long-term decrease in seasonal flooding forced by the precession-controlled reduction in local insolation. Al and Si abundances are decoupled following a transition to deposition of 16 cm sand at 4.5 ka, with Al decreasing and Si increasing rapidly. This period of sand deposition represents the termination of the African Humid Period. The timing of this event is younger than the transition at 5.5 ka recorded in marine cores from ODP site 658 (offshore of Mauritania), possibly due to Lake Fati's location further to the south and closer to the present position of the Intertropical Convergence Zone. The transition to sand deposition in the Lake Fati core is abrupt (< 40 years), but follows increasing Fe abundance for circa 200 years that could indicate gradual drying preceding this transition. A 6 cm layer of mud at the top of the core indicates the establishment of the current lake system roughly 200 years ago.

100 Years of benthic foraminiferal history on the inner Texas shelf inferred from fauna and stable isotopes: Preliminary results from two cores

by Josiah Strauss

Co-authored with Ethan Grossman, Joseph Carlin, Timothy Dellapenna

Coastal regions, such as the Texas–Louisiana shelf, are subject to seasonal hypoxia that strongly depends on the... more Coastal regions, such as the Texas–Louisiana shelf, are subject to seasonal hypoxia that strongly depends on the magnitude of freshwater discharge from local and regional river systems. We have determined benthic foraminiferal fauna and isotopic compositions in two 210Pb dated box cores (BR4 and BR5) to examine the evidence for nearshore hypoxia and freshwater discharge on the Texas shelf during the last 100years. The 210Pb chronologies of both cores reveal sedimentation rates of 0.2 and 0.1 cm yr−1, translating to ∼60 and ∼90 yearrecords. The fauna of both cores were almost exclusively composed of Ammonia parkinsoniana and Elphidium excavatum, indicating euryhaline ambient waters. The Ammonia–Elphidium (A–E) index, a qualitative measure of low oxygen conditions, shows an increase from values between 20 and 50 to near 100 in both cores, suggesting low oxygen conditions between 1960 and the core top. Between 1950 and 1960 (9–10 cm), low A–E values in BR4 coincide with high δ18O and δ13C values greater than 0‰ and −1‰ respectively. This event corresponds to severe drought (the Texas Drought of Record) over the Brazos River drainage basin and considerably reduced river discharge from 1948 to 1957. High A–E values prior to this event imply low-oxygen conditions were prevalent prior to anthropogenic exacerbation of Louisiana shelf hypoxia and at least since the dredging of a new Brazos River delta in 1929. Elphidium excavatum δ13C values are very low (−4‰) and indicative of significant vital effect. The δ13C values of A. parkinsoniana average −3‰ and exhibit little variability, most likely reflecting pore waters influenced by aerobic and anaerobic respiration. The association of lowered Brazos River discharge with more oxygenated shelf bottom waters suggests Brazos River discharge and shelf hypoxia are linked, but the influence of Mississippi–Atchafalaya discharge can also contribute to shelf stratification.

Homogeneous magnesium isotopic composition of seawater: an excellent geostandard for Mg isotope analysis

by Josiah Strauss

The sea level conundrum: Insights from paleo studies

by Alex Thomas

Penultimate deglacial sea-level timing from uranium/thorium dating of Tahitian corals

by Alex Thomas

Constant bottom water flow into the Indian Ocean for the past 140 ka indicated by sediment 231Pa/230Th ratios

by Alex Thomas

Reversed flow of Atlantic deep water during the Last Glacial Maximum

by Alex Thomas

Formation of “Southern Component Water” in the Late Cretaceous: Evidence from Nd-isotopes

by Daniel Murphy

Cretaceous deep-water formation in the Indian sector of the Southern Ocean

by Daniel Murphy

Published in Paleoceanography, 2012

The role that meridional overturning circulation (MOC) patterns played in poleward heat transport during the extreme... more The role that meridional overturning circulation (MOC) patterns played in poleward heat transport during the extreme warmth of the Early to Late Cretaceous is a fundamental and unresolved question in climate dynamics. In order to address this question we must determine where deep waters formed, and how they may have circulated during periods of extreme warmth. Here we present late Albian through Maastrichtian (105 to 65 Ma) Nd isotope records from Deep Sea Drilling Project (DSDP) and Ocean Drilling Program (ODP) sites in the proto-Indian Ocean and the tropical Pacific. Comparison of these data with previously published records indicates deep-water formation in the Indian sector of the Southern Ocean began at least
105 Ma, extending the record of high-latitude convection back into the Early Cretaceous prior to the peak warmth of the mid-Cretaceous.  The growing body of data supports a mode of MOC in part characterized by high-latitude downwelling during the peak of greenhouse warmth of the Mesozoic and Cenozoic.
However, this mode of MOC likely was characterized by numerous locations of deep convection that were regionally important, but not significant in terms of a globally overturning circulation due to paleogeographic and bathymetric barriers.

Toarcian black shales in the Dutch Central Graben: record of energetic variable depositional conditions during an oceanic anoxic event

by João Trabucho-Alexandre

published in 'Journal of Sedimentary Research', 2012

The environmental conditions, mechanisms, and processes that resulted in the deposition of organic-matter-rich... more The environmental conditions, mechanisms, and processes that resulted in the deposition of organic-matter-rich sediments during the early Toarcian oceanic anoxic event are still a matter of discussion. A petrographic and geochemical study was carried out using Posidonia Shale Formation (lower Toarcian) black shale samples from two wells located offshore The Netherlands in the Dutch Central Graben. This formation is a lateral equivalent of Toarcian black shale successions in northern Europe. The lower Toarcian black shales in the Dutch Central Graben exhibit a variety of depositional fabrics, sedimentary structures, and textures that indicate dynamic energetic conditions at the time of their deposition and appear to have been deposited mostly by bottom currents rather than settling from pelagic suspension. The Posidonia Shale Formation black shales are characterized by normally graded thin beds (, 10 mm thick) with erosional bases wherein cross-lamination is very common. The tops of these thin beds are commonly bioturbated. These observations are in contrast with the traditional interpretation of the deposition of lower Toarcian black shales as having taken place under a stagnant, anoxic water column via suspension settling. Black shales are commonly more heterogeneous than normally assumed and are the product of diverse sedimentary processes. Geochemical results, in combination with petrography, suggest that productivity and high accumulation rates of reactive organic matter were behind the establishment of sediment anoxia. The most organic-matter-rich shales, which are characterized by redox-element anomalies, are cross-laminated, thin-bedded shales, and each thin bed was deposited quickly, thus favoring the preservation of organic matter. The petrographic study of black shales complements geochemical data because geochemical analysis of sedimentary rocks, however high-resolution, always represents an averaging of environmental conditions at the time of deposition over at least several hundreds of years.

Environmental versus biological controls on Mg/Ca variability in Globigerinoides ruber (white) from core top and plankton tow samples in the southwest Pacific Ocean

by Annette Bolton

Published in Paleoceanography

Laser ablation inductively coupled plasma mass spectrometry was used to analyze the
individual chambers from... more Laser ablation inductively coupled plasma mass spectrometry was used to analyze the
individual chambers from tests of foraminiferal fossil and plankton tow Globigerinoides
ruber from the southwest Pacific Ocean, from latitudes 3°S to 42°S. The variability of
Mg/Ca between chambers of an individual (intraindividual) and individuals of the same
population (interindividual), is such that when converted to temperature, the extent of
intra‐individual and interindividual variability appears to exceed that attributable to either
calcification or seasonal temperature variability. The pooled mean chamber Mg/Ca
from each core top and plankton tow site demonstrates a significant (p < 0.05) positive
correlation with temperature. We derive chamber‐specific calibrations where Mg/CaCh_F‐2 =
0.798 exp0.070 T, Mg/CaCh_F‐1 = 0.891 exp0.067 T and Mg/CaCh_F = 0.590 exp0.072 T.
We do not observe any bias between the two morphotypes Gs. ruber ruber and Gs. ruber
pyramidalis. The chamber‐specific calibrations potentially offset Mg/Ca‐based temperature
reconstructions if used on bulk (whole) test Mg/Ca or applied to misidentified chambers.
Nevertheless, these calibrations can be used to reliably estimate sea surface temperature.
Although there is a general overriding temperature control on Mg/Ca, we show that removal
of the effect of temperature at each site reveals a lognormal Mg/Ca distribution. This
suggests that Mg/Ca variability at each site is also affected by biological mechanism(s)
that may control the distribution of interindividual Mg/Ca. In addition, other TE/Ca data
(Al/Ca and Mn/Ca) from laser ablation trace element depth profiles can be used to identify
detrital or diagenetic phases that may bias the trace element/Ca signal.

Strengthening of North American dust sources during the late Pliocene (2.7 Ma)

by David Naafs

Published in Earth and Planetary Science Letters

Here we present orbitally-resolved records of terrestrial higher plant leaf wax input to the North Atlantic over the... more Here we present orbitally-resolved records of terrestrial higher plant leaf wax input to the North Atlantic over the last 3.5 Ma, based on the accumulation of long-chain n-alkanes and n-alkanl-1-ols at IODP Site U1313. These lipids are a major component of dust, even in remote ocean areas, and have a predominantly aeolian origin in distal marine sediments. Our results demonstrate that around 2.7 million years ago (Ma), coinciding with the intensification of the Northern Hemisphere glaciation (NHG), the aeolian input of terrestrial material to the North Atlantic increased drastically. Since then, during every glacial the aeolian input of higher plant material was up to 30 times higher than during interglacials. The close correspondence between aeolian input to the North Atlantic and other dust records indicates a globally uniform response of dust
sources to Quaternary climate variability, although the amplitude of variation differs among areas. We argue that the increased aeolian input at Site U1313 during glacials is predominantly related to the episodic appearance of continental ice sheets in North America and the associated strengthening of glaciogenic dust sources. Evolutional spectral analyses of the n-alkane records were therefore used to determine the dominant
astronomical forcing in North American ice sheet advances. These results demonstrate that during the early Pleistocene North American ice sheet dynamics responded predominantly to variations in obliquity (41 ka), which argues against previous suggestions of precession-related variations in Northern Hemisphere ice sheets during the early Pleistocene.

Sijinkumar, A.V., Nath, B.N., Guptha, M.V.S., (2010) Late Quaternary record of pteropod preservation from the Andaman Sea. Marine Geology 275, 221-229, doi:10.1016/j.margeo.2010.06.003.

by Sijin Kumar

Coral windows onto seasonal climate variability in the northern Caribbean since 1479

by Hali Kilbourne

800,000 years of abrupt climate variability - supporting online material

by Martin Ziegler

published in Science, 2011

Paleotemperature and paleosalinity inferences and chemostratigraphy across the Aptian/Albian boundary in the subtropical North Atlantic

by Darren Gröcke

Paleoceanography, 26, PA4221, doi:10.1029/2011PA002178

Geochemical analyses of extraordinarily well preserved late Aptian–early Albian foraminifera from Blake Nose (Ocean... more Geochemical analyses of extraordinarily well preserved late Aptian–early Albian foraminifera from Blake Nose (Ocean Drilling Program Site 1049) reveal rapid shifts of δ18O, δ13C, and 87Sr/88Sr in the subtropical North Atlantic that may be linked to a major planktic foraminifer extinction event across the Aptian/Albian boundary. The abruptness of the observed geochemical shifts and their coincidence with a sharp lithologic contact is explained as an artifact of a previously undetected hiatus of 0.8–1.4 million years at the boundary contact, but the values before and after the hiatus indicate that major oceanographic changes occurred at this time. 87Sr/88Sr increase by ~0.000 200, δ13C values decrease by 1.5‰ to 2.2‰, and δ18O values decrease by ~1.0‰ (planktics) to 0.5‰ (benthics) across the hiatus. Further, both 87Sr/88Sr ratios and δ18O values during the Albian are anomalously high. The 87Sr/88Sr values deviate from known patterns to such a degree that an explanation requires either the presence of inter-basin differences in seawater 87Sr/88Sr during the Albian or revision of the seawater curve. For δ18O, planktic values in some Aptian samples likely reflect a diagenetic overprint, but preservation is excellent in the rest of the section. In well preserved material, benthic foraminiferal values are largely between 0.5 and 0.0‰ and planktic samples are largely between 0.0‰ to –1.0‰, with a brief excursion to –2.0‰ during OAE 1b. Using standard assumptions for Cretaceous isotopic paleotemperature calculations, the δ18O values suggest bottom water temperatures (at ~1000–1500 m) of 8–10°C and surface temperatures of 10–14°C, which are 4–6°C and 10–16°C cooler, respectively, than present day conditions at the same latitude. The cool subtropical sea surface temperature estimates are especially problematic because other paleoclimate proxy data for the mid-Cretaceous and climate model predictions suggest that subtropical sea surface temperatures should have been the same as or warmer than at present. Because of their exquisite preservation, whole scale alteration of the analyzed foraminifera is an untenable explanation. Our proposed solution is a high evaporative fractionation factor in the early Albian North Atlantic that resulted in surface waters with higher δ18O values at elevated salinities than commonly cited in Cretaceous studies. A high fractionation factor is consistent with high rates of vapor export and a vigorous hydrological cycle and, like the Sr isotopes, implies limited connectivity among the individual basins of the Early Cretaceous proto-Atlantic ocean.

Sea level controls sedimentation and environments in coastal caves and sinkholes

by Darren Gröcke

Marine Geology, 286, 35–50, doi:10.1016/j.margeo.2011.05.004

Quaternary climate and sea-level research in coastal karst basins (caves, cenotes, sinkholes, blueholes, etc.)... more Quaternary climate and sea-level research in coastal karst basins (caves, cenotes, sinkholes, blueholes, etc.) generally focuses on analyzing isotopes in speleothems, or associating cave elevations prior sea-level highstands. The sediments in coastal karst basins represent an overlooked source of climate and sea-level information in the coastal zone, but to accurately interpret these sediments first requires an understanding of the forcing mechanisms that emplace them. In this study, we hypothesize that coastal karst basins transition through vadose, littoral, anchialine, and finally into submarine environments during sea-level rise because groundwater and sea level oscillate in near synchrony in the coastal zone, causing each environment to deposit a unique sedimentary facies. To test this hypothesis, the stratigraphy in twelve sediment cores from a Bermudian underwater cave (Green Bay Cave) was investigated and temporally constrained with twenty radiocarbon dates. The results indicate that we recovered the first succession spanning the entire Holocene from an underwater cave (~13 ka to present). The sediments were characterized with X-radiography, fossil remains, bulk organic matter, organic geochemistry (δ13Corg, C:N), and grain size analysis. Four distinct facies represent the four depositional environments: (i) vadose facies (> 7.7 ka, calcite rafts lithofacies), (ii) littoral facies (7.7 to 7.3 ka: calcite rafts and mud lithofacies), (iii) anchialine facies (7.3 to 1.6 ka: slackwater and diamict lithofacies), and (iv) submarine facies (< 1.6 ka: carbonate mud and shell hash lithofacies). The onset and duration of these sedimentary depositional environments are closely linked to Holocene sea-level rise in Bermuda, indicating that sea level controls environmental development in coastal karst basins. Finally, we present a conceptual model for interpreting the sediments and environments in coastal karst basins as a result of sea-level change.

The significance of an Early Jurassic (Toarcian) carbon-isotope excursion in Haida Gwaii (Queen Charlotte Islands), British Columbia, Canada

by Darren Gröcke

Earth & Planetary Science Letters, 307, 19–26, doi:10.1016/j.epsl.2011.04.013

During the Early Toarcian there was a significant disruption in the short-term active carbon reservoir as revealed by... more During the Early Toarcian there was a significant disruption in the short-term active carbon reservoir as revealed by carbon-isotope records, which show a broad positive shift that is interrupted by a large 5–7‰ negative excursion (δ13Corg). Carbon-isotope excursion co-occurs with the deposition of organic-rich shales in many areas. This perturbation in carbon isotopes is thought to be indicative of severe climate change and marine anoxia. The two leading hypotheses as to the cause of this event invoke either global or regional controls. Here we present carbon-isotope data from Haida Gwaii, British Columbia, Canada showing a significant perturbation within a temporally constrained Early Toarcian succession that was deposited in the northeastern paleo-Pacific Ocean. These data reinforce the concept that the short-term active carbon reservoir was affected globally, and assist with the correlation of ammonite zonal schemes between western North America and Europe. The δ13Corg data show a broad positive shift that is interrupted by a sharp and pronounced negative excursion of 7‰ (8.5‰ in δ13Cwood) in the Early Toarcian Kanense Zone. This negative excursion also coincides with increasing total organic carbon (TOC) from ~0.4% to ~1.2%. These data suggest that the Early Toarcian carbon-isotope perturbation was indeed global and imprinted itself on all active global reservoirs of the exchangeable carbon cycle (deep marine, shallow marine, atmospheric).