Carlo Laj

• Ecole Normale Supérieure de Paris

The South China Sea, located at the transition between the Pacific and the Indian Ocean, receives every year, mainly during the rain season, enormous amounts of river sediments originating from the erosion/weathering of rocks in the catchment basins. At sea, these sediments are carried by different water masses to their deposition site and they con...

A sequence of tephra layers is studied in a 13.9 m-long deep-sea core (MD01-2474G) from the southern Tyrrhenian Sea. The chronology of the succession is provided by a high-resolution age-depth model based on isotope stratigraphy and AMS radiocarbon dating, which place the succession of events in a time interval spanning the last 70 ka. Based on a p...

New absolute paleomagnetic intensity (PI) are investigated from 37 lava flows located at Tenerife and Gran Canaria (Canary Islands). They complete previously published directional results from the same flows and therefore allow to examine the time variations of the full geomagnetic vector. Twenty-eight flows are radiocarbon dated between 1706 AD an...

We report on new paleomagnetic directions obtained from 38 lava flows located at Tenerife and Gran Canaria (Canary Islands, Spain). One flow is a historical one (1706 AD) and 28 other flows are dated by radiocarbon between 1550 AD and about 13 200 BC. Nine other flows are not dated but they have stratigraphic links with the other flows. Thermomagne...

The late Pleistocene and Holocene laminated marine sediments deposited in Saanich Inlet, British Columbia, contain a well-known annually resolved record of environmental change. In this paper, these sediments were analyzed for the first time with an Itrax micro-X-ray fluorescence core scanner with a resolution of 100 μm. These analyses were complem...

During the last glacial period, the North Atlantic regionexperienced pronounced, millennial-scale alternations between cold, stadial conditions and milder interstadial conditions--commonly referred to as Dansgaard-Oeschger oscillations--as well as periods of massive iceberg discharge known as Heinrich events. Changes in Northern Hemisphere temperat...

During the last glacial period, the North Atlantic region experienced pronounced, millennial-scale alternations between cold, stadial conditions and milder interstadial conditions-commonly referred to as Dansgaard-Oeschger oscillations-as well as periods of massive iceberg discharge known as Heinrich events. Changes in Northern Hemisphere temperatu...

Paleomagnetic secular variation (PSV) bear great information on the geodynamo field of the Earth's interior and can be used for stratigraphic correlation on a regional scale. In this study, we constructed PSV curve of rapidly deposited Holocene marine sequence (Core MD06-3040) from the mud sediments on the East China Sea (ECS) inner continental she...

Carlo E. Laj received the Excellence in Geophysical Education Award at the 2011 AGU Fall Meeting Honors Ceremony, held on 7 December in San Francisco, Calif. The award honors “a sustained commitment to excellence in geophysical education by a team, individual, or group.”

Paleomagnetic study on marine sediments can provide continuous, high-resolution records of short-term fluctuations of the Earth's magnetic field, which can be used for inter-core correlations at regional scale. However, Holocene paleomagnetic secular variation (PSV) records from marine sediment are still rare. Detailed paleomagnetic and rock magnet...

The Laschamp excursion, originally identified by N. Bonhommet in the French Massif Central, has been intensively investigated worldwide. Based on its short duration, this excursion has been very often used as a chronostratigraphic tiepoint by different communities. Recently, however, Plenier et al., (2007) have proposed a duration of about 6000 yea...

Glacial millennial-scale paleoceanographic changes in the Southeast Pacific and the adjacent Southern Ocean are poorly known due to the scarcity of well-dated and high resolution sediment records. Here we present new surface water records from sediment core MD07-3128 recovered at 53°S off the Pacific entrance of the Strait of Magellan. The alkenone...

We present a coupled paleomagnetic/dating investigation conducted on three different lava flows from the island of Tenerife (Canary Islands; Spain) erupted during the Mono Lake excursion (MLE). Paleomagnetic analyses consist in zero field demagnetizations (AF and/or thermal) and of Thellier and Thellier experiments using the PICRIT-03 set of criter...

We present sea surface, upper thermocline, and benthic delta O-18 data, as well as temperature and paleoproductivity proxy data, from the International Marine Global Change Study Program (IMAGES) Core MD06-3067 (6 degrees 31' N, 126 degrees 30' E, 1575 m water depth), located in the western equatorial Pacific Ocean within the flow path of the Minda...

We present sea surface, upper thermocline, and benthic d18O data, as well as temperature and paleoproductivity proxy data, from the International Marine Global Change Study Program (IMAGES) Core MD06-3067 (6°31'N, 126°30'E, 1575 m water depth), located in the western equatorial Pacific Ocean within the flow path of the Mindanao Current. Our records...

Glacial millennial-scale paleoceanographic changes in the Southeast Pacific and the adjacent Southern Ocean are poorly known due to the scarcity of well-dated and high resolution sediment records. Here we present new surface water records from sediment core MD07-3128 recovered at 53°S off the Pacific entrance of the Strait of Magellan. The alkenone...

The anisotropy of magnetic susceptibility (AMS), coupled with mineral magnetic identification, has been investigated in about 640 samples from 27 basaltic dikes of Tertiary age in Eastern Iceland. The dikes are a few meters thick and they have been sampled all across. Three types of magnetic fabrics with well-defined mean principal axes of anisotro...

High-resolution magnetic analysis was performed on the 19.22m core MD06-3040 (27°43.3663´N, 121°46.8822´E; 46m water depth) from the East China Sea (ECS) inner continental shelf, which was recovered during the IMAGES XIV MD155-Marco Polo 2 cruise of the R/V Marion Dufresne (IPEV). Magnetic grains are mainly transported to the inner shelf from erosi...

The western equatorial Pacific is a highly dynamic region, playing a significant role in both tropical and extra-tropical climates through its strong influence on the El Niño-Southern Oscillation (ENSO) phenomenon and the position of the Inter-tropical Convergence Zone (ITCZ). While the modern behaviours of these climate systems are reasonably well...

Since the last geomagnetic reversal, 780,000 years ago, the Earth's magnetic field repeatedly dropped dramatically in intensity. This has often been associated with large variations in local field direction, but without a persistent global polarity flip. The structure and dynamics of geomagnetic excursions, and especially the difference between exc...

The precise documentation of the natural variability of the THC during the interglacials in North Atlantic is of critical interest for the understanding of its future evolution under the effect of global warming. It is one of the goals of the AMOCINT project (06-EuroMARC-FP-008). We report on detailed magnetic analyses of a Holocene marine sequence...

A new record of a geomagnetic excursion has been obtained from Core MD07-3128 taken at (75° 34' W ; 52° 40' S) off the Pacific coast of Southern Chile, during the IMAGES XV-MD159-PACHIDERME cruise of the R/V Marion Dufresne (IPEV). Radiocarbon datings extend for the moment to 36.3 kyr BP at 18 meters. Linear extrapolation of the last 2 dates downco...

1] Sedimentary d 15 N records from the oligotrophic western equatorial Pacific (WEP) off Mindanao show that late Holocene sedimentary d 15 N is substantially lower than that of the early Holocene, following a gradual >3 % decrease that occurred between 7 and 3 kyrs ago. Analyses of modern day nitrate isotope profiles from the same region indicate t...

Several studies achieved during the last decade evidence the strong endeavor to push toward younger and younger ages the 40Ar/39Ar chronology. In parallel, all these progress have extended the scope of application of the 40Ar/39Ar chronology especially in paleoclimatic studies to provide Astronomical independent ages for oxygen isotope stages. Most...

The precise documentation of the natural variability of the THC during the interglacials in North Atlantic is of critical interest for the understanding of its future evolution under the effect of global warming. We report on detailed magnetic analyses of the entire Holocene period from several marine sequences distributed from northern to southern...

A record of a geomagnetic excursion has been obtained from Core MD07-3128 taken at (52 degrees S) off the Pacific coast of Southern Chile, during the IMAGES XV-MD159-PACHIDERME cruise of the R/V Marion Dufresne (IPEV). The primary component of magnetization has been isolated after AF demagnetization beyond 20 mT, after removal of a strong (80 per c...

Reductive diagenesis on magnetic minerals has been increasingly documented in coastal and continental shelf sediments, which is mostly characterized by a sharp decrease of all magnetic parameters at shallow depth and sometimes by two steplike decreases depending on the stability of magnetic minerals and chemical environment of the sediments. Magnet...

Geomagnetic excursions were generally treated with skepticism as recently as 20 years ago; however, as the global distribution of excursion records and quality of their age control have improved, excursions are being integrated into the polarity timescale, at least for the last few million years. The best-documented excursions comprise paired polar...

We examine the magnetic mineral deposition in three cores located at midlatitude sites in the South Indian Ocean, in an area where sediment eroded from the Kerguelen-Crozet plateau and transported by the marine currents, principally the Antarctic Circum Current, accumulates at a high sedimentation rate. We focus on Marine Isotopic Stage 3, characte...

We have obtained detailed geomagnetic paleointensity records from 3 high sedimentation rate cores from the North Atlantic. The three records have a very large coherency. AMS 14C dates and bulk magnetic parameters were used to inter-correlate the cores and to obtain a stack covering the 2-10 kyr interval. This stack appears to have reliably recorded...

Past changes in the monsoon activity and their consequences in terms of balance between erosion and chemical weathering on land have been investigated with success in the Indian ocean using magnetic properties of marine sediments. Farther east, only scarce data have been accumulated so far. Here, we present a first study of the magnetic properties...

A borehole core through the Holocene sediments of Saanich Inlet (British Columbia, Canada) was analyzed using high-resolution spectrophotometry to determine whether spectral–signal variations can be used as environmental/climatic proxies. The effects of post-drilling oxidation and water loss on the core sample were assessed by comparing spectral me...

High-resolution magnetic analysis has been performed on the top ∼25 m of core MD99-2275 (66°33.06′N, 17°41.59′W; 440 m water depth) from the mid-outer shelf off North Iceland. This is a key boundary region for climate changes related to atmospheric and oceanographic variations influenced by the moving limit between the cold and warm water masses at...

The global paleointensity database is restricted by the high failure rate of paleointensity analyses. Excluding thermal alteration, failure is usually caused by the presence of multidomain grains and interactions among grains, two properties that can be identified using first-order reversal curve (FORC) diagrams. We measured FORC diagrams on sister...

The cause of the cooling event culminating at 8.2 kyr B.P. in the Summit ice records, and in particular the role of ocean dynamics in this event, is a matter of considerable debate. Only a few marine records of suitable quality for monitoring North Atlantic Deep Water (NADW) properties during this climatic anomaly are available-making it difficult...

New Holocene geomagnetic paleointensity records have been constructed from the Western Antarctic Peninsula (WAP), Eastern Antarctic Peninsula (EAP), and from the East Antarctic Margin (EAM). The goal of this work is to develop Antarctic paleointensity reference curves for correlation and dating of Antarctic continental shelf sediments. Sediment seq...

Palaeomagnetic samples have been collected by the USGS from 16 radiocarbon-dated surface lava flows spanning 0-4.5 kyr on the Big Island, Hawaii. 5 cores from each individual site were assigned to Thellier-Thellier (thermal) palaeointensity analysis; 3 for microwave analysis. The two palaeointensity methods differ in the way energy is transferred t...

Paleointensity data are vital for a better knowledge of deep-earth processes. The paleointensity database is limited by the high failure rate of paleointensity analysis. Excluding thermal alteration, failure is usually caused by the presence of multi-domain (MD) grains and interactions among grains, two properties that can be identified using first...

The age of the Laschamp geomagnetic excursion has been recently re-investigated using unspiked K/Ar and Ar/Ar techniques (Guillou et al., Session V01, this conference). The new age determination of 40.4 +/- 2.0 ka (2 sigma) is more precise than those previously reported in the literature and agrees precisely with that deduced from the GLOPIS-75 sed...

During the last 25,000 years there has been low secular variation in the Pacific region. A large directional dataset for this specific time window already exists but will be enlarged by the inclusion of results from our recent analysis of rocks from Hawaii. In addition to the directional data, we have also obtained paleointensity values for a signi...

High resolution magnetic analysis has been performed on the top 25 m of core MD99-2275 (66°33.06'N, 17°41.59'W; 440 m water depth) taken with the R. V. Marion Dufresne from the mid- outer shelf off North Iceland. This is a key boundary region for climate changes related to atmospheric and oceanographic variations, influenced by the moving limit bet...

Precise documentation of the evolution of the thermohaline circulation (THC) during the Holocene period is raising an increasing interest among the community. Model studies suggest that the strength of the deep water current in North Atlantic is tightly linked to the formation rate of deep-water via the meridional transport of ocean heat. The under...

The origin of geomagnetic excursions has been debated ever since their discovery. Several testable mechanisms for excursions have been suggested: (i) if an excursion represents a significant departure of the dipole field from the rotation axis, it would be expected to have a global manifestation with similar VGP paths; (ii) if excursions occur when...

The Iceland Basin event (IBE), which is named for a record from ODP Site 983 in the North Atlantic Ocean (60.5°N), is a focus of growing interest in our community. This geomagnetic excursion is coeval with the marine oxygen isotope (MIS) stage 7/6 boundary at about 190 ka according to the orbitally tuned SPECMAP time scale. We have detailed new rec...

We present a compilation of paleointensity results from the Hawaiian long basaltic cores HSDP1 (Mauna Loa and Mauna Kea volcanos), SOH-4 and SOH-1 (Kilauea Volcano) and the first results from the aerial part of the new core HSDP2 (Mauna Loa and Mauna Kea volcanos). The results are selected using a set of paleointensity selection criteria (PICRIT-03...

We have obtained a global relative paleointensity stack using a selection of published records from marine cores with sedimentation rates in excess of 7 cm/kyr, from the North and South Atlantic Oceans, the Mediterranean and the Indian Ocean. After correlation of the cores, the results were stacked using a new approach to minimize possible local di...

New high resolution records of bulk magnetic parameters (ARM, IRM, and low field susceptibility) of cores taken in the South Indian Ocean, northeast of the Kerguelen plateau document a coherent signature during the last glacial epoch and the previous interglacial, with marked variations at a millennial scale. We interpret this signal as tracing pas...

Precise documentation of past variations in the strength of thermohaline circulation (THC) is critical for the understanding of the mechanisms and dynamics of changes in climate and carbon cycle. Here we present a record of changes in the strength of the North Atlantic bottom current obtained from a mineral magnetic study of high accumulation rate...

A total of 113 paleomagnetic sites were sampled along an Anatolian S–N transect from the Arabian platform, the Hatay region, the Eastern Taurides, the Kirsehir block, the Sivas basin and the Eastern Pontides. Reliable characteristic remanent paleomagnetic directions were retrieved from 37 of these sites, spanning in time from Paleocene to Miocene....

We have obtained new relative geomagnetic paleointensity records from high accumulation rate sediments in the Atlantic Ocean and in the Mediterranean Sea. Measurements were made using either u-channel samples or standard 2x2x2 cm single samples. A minimum of 10 steps of demagnetization was used to characterize the NRM and the ARM. The ratio NRM/ARM...

Paleointensity records from sediments are often stacked to minimize possible local effects due to deposition/environnemental conditions at different sites which may locally affect the fidelity of the records. The fidelity/reliability of each individual record may however change along the sedimentary column, so that in a given time interval, one rec...

The Indian/Asian monsoon is one of the major component of the tropical climate system. By contrast with the Arabian Sea and the Indian Ocean, the South China Sea, under the influence of the East Asian Monsoon, has been little investigated. Here we report results for the last 1.18 Myr obtained from Site 1146 (ODP Leg 184) in the South China Sea. Cha...

Relative paleointensity records are usually obtained from sediments by directly normalizing the NRM by the susceptibility or by the laboratory induced ARM or IRM. This procedure, however, allows to retrieve reliable paleointensity records only when the magnetic carrier is magnetite exhibiting rather limited changes in abundance and grain-size along...

New records of past sea surface temperatures (SSTs) were derived in the 30–50 kyr B.P. time interval from a core located at 45°S in the Southern Indian Ocean, MD94-103. To investigate the climatic phasing between the Southern Indian Ocean, the Greenland and the Antarctic ice, the magnetic signal of core MD94-103 was synchronized at better than mill...

We present simulated records of past changes in the atmospheric Δ14C for the last 50 kyr due to changes in geomagnetic field intensity and in the strength of the North Atlantic Deep Water (NADW). A new geomagnetic record was used, largely based on the NAPIS-75 record [Laj et al., Phil. Trans. R. Soc. London A 358 (2000) 1009–1025] which has been ex...

Recent coring of high-deposition-rate Atlantic sediments has led to the development of North Atlantic (NAPIS) and South Atlantic (SAPIS) geomagnetic paleointensity stacks. The SAPIS stack comprises five records from the sub-Antarctic South Atlantic (41–47°S, 6–10°E). Four are from piston cores collected during the Ocean Drilling Program (ODP) Leg 1...

Reliable Thellier–Thellier paleointensity determinations were obtained from 321 (out of 766 examined) samples from the upper 200 units (675m) of core SOH-4 drilled in the Kilauea volcano. The main trend of the SOH-4 record is a marked decrease from values higher than present in the last 4kyr to values about 40% smaller from about 20kyr to the botto...