ALBERT

Description: Despite a clear correlation of alkenone unsaturation and sea surface temperatures (SST) throughout most parts of the ocean, scatter of the regression for various calibration equations has been shown to increase significantly at low SSTs. In this study we combine previously published ( n = 101) and new ( n = 51) surface sediment data from the northern North Atlantic to constrain uncertainties of alkenone paleothermometry at low SSTs and to discuss possible sources of the increased scatter in the regression. The correlation between alkenone unsaturation and SSTs is strongest, in particular at the cold end (SSTs 〈10°C), when the tetra-unsaturated alkenones (C 37:4 ) are included in the unsaturation index (expressed as ) and regressed against spring-summer temperature. Surface ocean salinity and sea ice cover are not correlated with per se . However, samples located in regions of permanent winter sea ice cover exhibit a significant warm bias. Deviation from the linear regression is posited to be related to a number of additional non-exclusive factors, such as advection of allochthonous material, local temperature stratification, and uncertainty in the absolute age of surface sediment samples assumed to be equivalent to modern conditions. We conclude that alkenone unsaturation allows accurate reconstruction of SST records from many regions of the North Atlantic if the factors confounding alkenone paleothermometry detailed here can be excluded. This article is protected by copyright. All rights reserved.

Description: Despite a clear correlation of alkenone unsaturation and sea surface temperatures (SST) throughout most parts of the ocean, scatter of the regression for various calibration equations has been shown to increase significantly at low SSTs. In this study, we combine previously published (n = 101) and new (n = 51) surface sediment data from the northern North Atlantic to constrain uncertainties of alkenone paleothermometry at low SSTs and to discuss possible sources of the increased scatter in the regression. The correlation between alkenone unsaturation and SSTs is strongest, in particular at the cold end (SSTs 〈 10°C), when the tetra-unsaturated alkenones (C37:4) are included in the unsaturation index (expressed as inline image) and regressed against spring-summer temperature. Surface ocean salinity and sea ice cover are not correlated with inline image per se. However, samples located in regions of permanent winter sea ice cover exhibit a significant warm bias. Deviation from the linear regression is posited to be related to a number of additional non-exclusive factors, such as advection of allochthonous material, local temperature stratification, and uncertainty in the absolute age of surface sediment samples assumed to be equivalent to modern conditions. We conclude that alkenone unsaturation allows accurate reconstruction of SST records from many regions of the North Atlantic if the factors confounding alkenone paleothermometry detailed here can be excluded.

Description: Unique marine sediment cores retrieved from the southwestern slope of the Iceland‐Faroe Ridge (IFR), close to the main axis of the Iceland‐Scotland Overflow Water (ISOW) revealed prominent sedimentary cycles reflecting near‐bottom current dynamics, sediment transport and deposition, coincident with Dansgaard‐Oeschger cycles and deglacial perturbations of the Atlantic Meridional Overturning Circulation (AMOC). The transition between Greenland Stadials (GSs) and Greenland Interstadials (GIs) follows a distinct, recurring sedimentation pattern. Basaltic (Ti‐rich) silts were transported from local volcanic sources by strong bottom currents and deposited during GIs comparable to modern ocean circulation. Finer‐grained felsic (K‐rich) sediments were deposited during GSs, when ISOW was weak. Possible felsic source areas include British‐Ireland and/or Fennoscandian shelf areas. A cyclic saw‐tooth pattern of bottom current strength is characterized by gradual intensification during GIs followed by a sharp decline towards GSs as is documented at core sites along the flank of Reykjanes Ridge. The cores north of Faroe Channel instead document the opposite pattern. This suggests that the near‐bottom currents along the Reykjanes Ridge are strongly controlled by the flow cascading over the IFR. Heinrich (like) Stadials (HSs) especially HS‐1 and HS‐2 are characterized by the deposition of very fine felsic sediments pointing to weakened bottom currents. Distinct coarse‐grained intervals of ice rafted debris (IRD) are absent from the sediment records, although pebble and gravel sized IRD is irregularly distributed throughout the fine sediment matrix. Near bottom currents are considered to have a major control on the lithogenic sediment deposition southwest of the Iceland‐Faroe Ridge and further down‐stream.

Description: The progress of science is tied to the standardization of measurements, instruments, and data. This is especially true in the Big Data age, where analyzing large data volumes critically hinges on the data being standardized. Accordingly, the lack of community‐sanctioned data standards in paleoclimatology has largely precluded the benefits of Big Data advances in the field. Building upon recent efforts to standardize the format and terminology of paleoclimate data, this article describes the Paleoclimate Community reporTing Standard (PaCTS), a crowdsourced reporting standard for such data. PaCTS captures which information should be included when reporting paleoclimate data, with the goal of maximizing the reuse value of paleoclimate data sets, particularly for synthesis work and comparison to climate model simulations. Initiated by the LinkedEarth project, the process to elicit a reporting standard involved an international workshop in 2016, various forms of digital community engagement over the next few years, and grassroots working groups. Participants in this process identified important properties across paleoclimate archives, in addition to the reporting of uncertainties and chronologies; they also identified archive‐specific properties and distinguished reporting standards for new versus legacy data sets. This work shows that at least 135 respondents overwhelmingly support a drastic increase in the amount of metadata accompanying paleoclimate data sets. Since such goals are at odds with present practices, we discuss a transparent path toward implementing or revising these recommendations in the near future, using both bottom‐up and top‐down approaches.