Patrizia Macrì

Environmental magnetism of Antarctic Late Pleistocene sediments and interhemispheric correlation of climatic events

Abstract Recent developments in paleomagnetism and environmental magnetism provide new tools for the detailed correlation of climatically induced magnetic mineralogy changes in sedimentary sequences. Studies of these changes contribute to the reconstruction of climate history for the glacial–interglacial cycles of the Late Pleistocene and to the delineation of the range of natural variability for global climate during the past hundred thousands years. Here we show that sharp coercivity minima observed in fine-grained sediments from the continental rise of the western Antarctic Peninsula correlate to the major rapid cooling events of the northern Atlantic (Heinrich layers). We interpret such an environmental magnetic signal in terms of variations in deep sea diagenetic processes of sulfide formation, which reflect changes in the input of detrital organic matter controlled by sea-ice extent. With the inherent uncertainties in age controls, the sedimentary paleoclimatic markers of the two hemispheres are almost contemporaneous, but interhemispheric time lags or leads of the order of 1–2 kyr (such as those recently reported from the Greenland and Antarctic ice cores) are also compatible with the data.

Evidence for a variable paleomagnetic lock‐in depth in the Holocene sequence from the Salerno Gulf (Italy): Implications for “high‐resolution” paleomagnetic dating

We report on a paleomagnetic and rock magnetic study of two adjacent marine gravity cores from the Salerno Gulf (Italy), with measurements carried out on u-channel samples at 1-cm spacing. The cores recover a sedimentary sequence spanning, in the overlapping part, the last ∼6000 years and include a thick (∼1 m) pumice layer produced during the Somma-Vesuvius eruption of 79 A.D. Rock magnetic and lithostratigraphic data provide several tie-points for a detailed correlation between the two cores. Paleomagnetic data allow the determination of a well-defined characteristic remanent magnetization, with very similar stratigraphic trends and distinct features that can also be unambiguously correlated between the cores. However, the comparison of the various data sets points out that the paleomagnetic lock-in depth in the two adjacent cores varies through the stratigraphic succession. We discuss the implication of such results for assessing the potential of high-resolution paleomagnetic studies in dating sedimentary sequences on the basis of paleosecular variation of the geomagnetic field. In the studied case, the relative difference in the lock-in depth in the two cores causes “spreading” of the assigned paleomagnetic ages at a century scale.

Paleomagnetic evidence for a post–1.2 Ma disruption of the Calabria terrane: Consequences of slab breakoff on orogenic wedge tectonics

In the past few years, a wealth of paleomagnetic data gathered from Neogene sediments consistently showed that since ca. 10 Ma the Calabria terrane coherently drifted ~500 km ESE-ward from the Sardinian margin, and rotated 15°–20° clockwise (CW) as a rigid microplate between 2 and 1 Ma. Here we report on a high-resolution paleomagnetic investigation of the Crotone forearc basin of northern Calabria. The integrated calcareous plankton biostratigraphy indicates early Pliocene (Zanclean) to late early Pleistocene (Calabrian) ages for 29 successful paleomagnetic sites and/or sections. Unexpectedly, four domains undergoing distinct rotations are documented. Two blocks have undergone a CW rotation statistically undistinguishable, for both timing and magnitude, from the rigid Calabria rotation documented in the past. Two additional ~10-km-wide blocks yielded a 30.8° ± 22.5° and 32.0° ± 9.2° post–1.2 Ma counterclockwise rotation, likely due to left-lateral shear along two NW-SE fault zones. We infer that since advanced early Pleistocene times, after the end of the uniform CW rotation, left-lateral strike-slip tectonics disrupted the Calabria terrane, overwhelming a widespread extensional regime accompanying the Calabria drift since late Miocene times. Seismological evidence reveals that only the southern part of the Ionian slab subducting below Calabria is continuous, while beneath northern Calabria a slab window between 100 and 200 km depth is apparent. We suggest that the partial breakoff of the Ionian slab after 1 Ma induced the fragmentation of the Calabria wedge, and that strike-slip faults from the Crotone basin decoupled “inactive” northern Calabria from southern Calabria, still drifting towards the trench.

A Holocene paleosecular variation record from the northwestern Barents Sea continental margin

A high-resolution paleomagnetic and rock magnetic study has been carried out on sediment cores collected in glaciomarine silty-clay sequences from the continental shelf and slope of the southern Storfjorden trough-mouth fan, on the northwestern Barents Sea continental margin. The Storfjorden sedimentary system was investigated during the SVAIS and EGLACOM cruises, when 10 gravity cores, with a variable length from 1.03 m to 6.41 m, were retrieved. Accelerator mass spectrometry (AMS) 14C analyses on 24 samples indicate that the cores span a time interval that includes the Holocene, the last deglaciation phase and in some cores the last glacial maximum. The sediments carry a well-defined characteristic remanent magnetization and have a valuable potential to reconstruct the paleosecular variation (PSV) of the geomagnetic field, including relative paleointensity (RPI) variations. The paleomagnetic data allow reconstruction of past dynamics and amplitude of the geomagnetic field variations at high northern latitudes (75°–76° N). At the same time, the rock magnetic and paleomagnetic data allow a high-resolution correlation of the sedimentary sequences and a refinement of their preliminary age models. The Holocene PSV and RPI records appear particularly sound, since they are consistent between cores and they can be correlated to the closest regional stacking curves (UK PSV, FENNOSTACK and FENNORPIS) and global geomagnetic model for the last 7 ka (CALS7k.2). The computed amplitude of secular variation is lower than that outlined by some geomagnetic field models, suggesting that it has been almost independent from latitude during the Holocene.

The Istituto Nazionale di Geofisica e Vulcanologia Data Management System for the Arctic Sciences

The brokering approach can be successfully used to overcome the crucial question of searching among enormous amount of data (raw and/or processed) produced and stored in different information systems. In this paper, authors describe the Data Management System the DMS (Data Management System) developed by INGV (Istituto Nazionale di Geofisica e Vulcanologia) to support the brokering system GEOSS (Global Earth Observation System of Systems) adopted for the ARCA (Arctic Present Climate Change and Past Extreme Events) project. This DMS includes heterogeneous data that contributes to the ARCA objective (www.arcaproject.it) focusing on multi-parametric and multi-disciplinary studies on the mechanism (s) behind the release of large volumes of cold and fresh water from melting of ice caps. The DMS is accessible directly at the www.arca.rm.ingv.it, or through the IADC (Italian Arctic Data Center) at http://arcticnode.dta.cnr.it/iadc/gi-portal/index.jsp that interoperates with the GEOSS brokering system (http://www.geoportal.org/) making easy and fast the search of specific data set and its URL.