Search

Marine seismic reflection data have been collected for decades and since the mid-to late- 1980s much of this data is positioned relatively accurately. This older data provides a valuable archive, however, it is mainly stored on paper records that do not allow easy integration with other datasets. A method for converting these records to digital SEGY format has been reported previously, although the accuracy and reliability has not been documented. Using 3.5 kHz pinger, bathymetric and side scan sonar data we test the accuracy and data resolution of converted paper seismic records on the surface and shallow-subsurface of the Barra Fan, NE Atlantic Ocean. Frequencies of navigational updates and printed fix marks are vital in determining positional accuracy as interpolation between fixes, which may be 30 minutes apart, is a significant source of potential error. Vertical data resolution of the converted records is primarily governed by the dimensions of the printed record, with order of magnitude differences noted between the scanned BGS and NOC pinger records. Positional accuracy of pinger data is observed to be within the resolution of the bathymetric grid. BGS 1985 pinger data is located within 40 m of bathymetric constrained locations at 635 m below mean sea level and NOC 1998 pinger data within 25 m of bathymetric locations at 1180 m below mean sea level. This paper-to-digital conversion is not a replacement for modern data acquisition, but it does provide a valuable complement to such data. Where appropriate archival paper data is available for conversion it could be used to assist efficiency of forthcoming surveys and may be used to provide time series evidence of seabed processes. [ABSTRACT FROM AUTHOR]

Abstract: Planktic foraminiferal faunas (>150 µm) and stable isotopes from the last 15 kyr were studied in kasten core 13078#16 from the Porcupine Abyssal Plain, NE Atlantic (48°49.91 N, 16°29.94 W, water depth 4844 m) in order to document changes in surface waters. The faunas were dominated (>80%) by four species: Neogloboquadrina incompta (= N. pachyderma dextral), Globigerina bulloides, N. pachyderma (= N. pachyderma sinistral) and Globorotalia inflata and their abundances fluctuated strongly over the last 15 kyr. Other species, G. truncatulinoides (right and left-coiling forms) and Globigerinoides ruber (white), had low abundances (typically<6%). The polar species N. pachyderma dominated (~60%) the terminal glacial interval when surface conditions were cold, decreased to 25–35% during the deglaciation and remained low (<2%) throughout the Holocene. The relative abundance of N. incompta increased over the last 15 kyr and shows an inverse relationship with N. pachyderma. The increase in δ 13C values of G. bulloides, G. inflata and G. truncatulinoides over the last 15 kyr is consistent with the whole ocean shift due to the expansion of the terrestrial biosphere, indicating that the upper oceanic δ 13C values did not change significantly during this time. Between the deglaciation and the Holocene, the negative shift (~1.0‰) in δ 18O values of G. inflata and G. truncatulinoides equates to the global ice volume shift suggesting that there was no significant warming of the deeper surface waters or that the species migrated to occupy a similar temperature water mass during this time. In contrast, the negative shift (~1.7‰) in δ 18O values of G. bulloides corresponds to a local shift of 0.7‰, equivalent to a ~3 °C warming of surface waters. Between 10 kyr and 5 kyr, the positive δ 18O increases in G. inflata and G. truncatulinoides suggest a decrease in deeper surface water temperatures in the order of 1.0–1.5 °C, a change not evident in the shallow surface water δ 18O record of G. bulloides. Water mass stratification changes, revealed by the Δδ 18O G. inflata –G. bulloides and Δδ 18O G. truncatulinoides – G. bulloides records, suggest that the waters of the upper water column were more mixed during the last deglaciation than during the Holocene, and that there was a trend towards increasing water stratification over the last 15 kyr with a peak at ~4 kyr. Intervals of enhanced carbonate dissolution at ~12–8.5 kyr and ~4 kyr previously reported are not clearly reflected in changes in solution-susceptible planktic foraminiferal species, such as G. ruber. [Copyright &y& Elsevier]

Examines the composition and circulation of bottom water in the western Atlantic Ocean during the last glacial, based on pore-water analyses from the Amazon Fan. Geologic setting of the Amazon Fan; Surface sediments; Glacial-age sediments; Benthic foraminifers; Concentration of dissolved chloride.

Abstract: Variations in the strength of coastal upwelling in the South East Atlantic Ocean and summer monsoonal rains over South Africa are controlled by the regional atmospheric circulation regime. Although information about these parameters exists for the last glacial period, little detailed information exists for older time periods. New information from ODP Site 1085 for Marine Isotope Stages (MIS) 12–10 shows that glacial–interglacial productivity trends linked to upwelling variability followed a pattern similar to the last glacial cycle, with maximums shortly before glacial maxima, and minimums shortly before glacial terminations. During the MIS-11/10 transition, several periodic oscillations in productivity and monsoonal proxies are best explained by southwards shifts in the southern sub-tropical high-pressure cells followed by abrupt northwards shifts. Comparison to coeval sea-surface temperature measurements suggests that these monsoonal cycles were tightly coupled to anti-phased hemispheric climate change, with an intensified summer monsoon during periods of Northern (Southern) Hemisphere cooling (warming). The timing of these events suggests a pacing by insolation over precession periods. A lack of similar regional circulation shifts during the MIS-13/12 transition is likely due to the large equatorwards shift in the tropical convection zone that occurred during this extreme glaciation. [ABSTRACT FROM AUTHOR]

The southeast Atlantic Ocean is dominated by two major oceanic systems: the Benguela Upwelling System, one of the world's most productive coastal upwelling cells and the Agulhas Leakage, which is important for transferring warm salty water from the Indian Ocean to the Atlantic Ocean. Here, we present a multi-proxy record of marine sediments from ODP Site 1087. We reconstruct sea surface temperatures ( U 37 K ′ and TEX 86 indices), marine primary productivity (total chlorin and alkenone mass accumulation rates), and terrestrial inputs derived from southern Africa (Ti/Al and Ca/Ti via XRF scanning) to understand the evolution of the Southeast Atlantic Ocean since the late Pliocene. In the late Pliocene and early Pleistocene, ODP Site 1087 was situated within the Benguela Upwelling System, which was displaced southwards relative to present. We recognize a series of events in the proxy records at 3.3, 3.0, 2.2, 1.5, 0.9 and 0.6 Ma, which are interpreted to reflect a combination of changes in the location of major global wind and oceanic systems and local variations in the strength and/or position of the winds, which influence nutrient availability. Although there is a temporary SST cooling observed around the initiation of Northern Hemisphere glaciation (iNHG), proxy records from ODP Site 1087 show no clear climatic transition around 2.7 Ma but instead most of the changes occur before this time. This observation is significant because it has been previously suggested that there should be a change in the location and/or strength of upwelling associated with this climate transition. Rather, the main shifts at ODP Site 1087 occur at ca. 0.9 Ma and 0.6 Ma, associated with the early mid-Pleistocene transition (EMPT), with a clear loss of the previous upwelling-dominated regime. This observation raises the possibility that reorganisation of southeast Atlantic Ocean circulation towards modern conditions was tightly linked to the EMPT, but not to earlier climate transitions. [ABSTRACT FROM AUTHOR]

Subtropical gyre (STG) depth and strength are controlled by wind stress curl and surface buoyancy forcing 1,2 . Modern hydrographic data reveal that the STG extends to a depth of about 1 km in the Northwest Atlantic, with its maximum depth defined by the base of the subtropical thermocline. Despite the likelihood of greater wind stress curl and surface buoyancy loss during the Last Glacial Maximum (LGM) 3 , previous work suggests minimal change in the depth of the glacial STG 4 . Here we show a sharp glacial water mass boundary between 33° N and 36° N extending down to between 2.0 and 2.5 km-approximately 1 km deeper than today. Our findings arise from benthic foraminiferal δ 18 O profiles from sediment cores in two depth transects at Cape Hatteras (36-39° N) and Blake Outer Ridge (29-34° N) in the Northwest Atlantic. This result suggests that the STG, including the Gulf Stream, was deeper and stronger during the LGM than at present, which we attribute to increased glacial wind stress curl, as supported by climate model simulations, as well as greater glacial production of denser subtropical mode waters (STMWs). Our data suggest (1) that subtropical waters probably contributed to the geochemical signature of what is conventionally identified as Glacial North Atlantic Intermediate Water (GNAIW) 5-7 and (2) the STG helped sustain continued buoyancy loss, water mass conversion and northwards meridional heat transport (MHT) in the glacial North Atlantic., (© 2024. The Author(s).)