Fjord sediments are increasingly used as high-resolution archives of climate and environmental ch... more Fjord sediments are increasingly used as high-resolution archives of climate and environmental change, including variations in glacier mass balance and terrestrial hydrology. To accurately interpret such sediment records, it is crucial to comprehend sediment transport processes and determine sediment provenance. With this in mind, our main objective is to identify cost-effective parameters that can be used to reconstruct relative variations in the origin of sediments deposited in the Baker-Martínez fjord system, which is located between the Northern (NPI) and Southern (SPI) Patagonian Icefields. We focus on estimating the proportions of sediment derived from each icefield, taking advantage of the clearly distinct lithologies that underlie NPI (Patagonian Batholith) and SPI (Eastern Andean Metamorphic Complex) glaciers. The magnetic susceptibility and inorganic geochemistry of 21 surface sediment samples collected along the fjord system and that of suspended sediment samples from the...
Carbon Cycling in the Glacial Ocean: Constraints on the Ocean’s Role in Global Change, 1994
There are three fundamentally different proxies recording ocean productivity in sediments: those ... more There are three fundamentally different proxies recording ocean productivity in sediments: those representing flux (that is, export production), those representing nutrient concentrations (e.g., nitrate or phosphate), and those representing aspects of the trophic structure of the pelagic environment. Flux proxies disagree due to different power-law relationships to the source term. The particular power-laws (expressed in terms of proxy exponents) change as a function of geography, and may change as a function of time. Modification of the accumulation rate by changing preservation on the sea floor (and within the sediment) is an important aspect of this problem.
ABSTRACT The Red Sea is an oligotrophic water body with special characteristics due to its enclos... more ABSTRACT The Red Sea is an oligotrophic water body with special characteristics due to its enclosed position. There is almost no rainfall, no permanent rivers flowing into the Red Sea, and evaporation is high especially during winter. Phytoplankton is scarce in the oligotrophic Red Sea and dominated by small cells. There is no information on siliceous microorganisms preserved in the sediments of the Red Sea. Here we compare siliceous assemblages (mainly diatoms) from plankton tows and sediments collected along a N-S profile (28^o to 21^oN), and from the Shaban Deep, a brine-filled basin in the central axis of the Red Sea. The goal is to assess the effects of preservation and the accuracy with which the sedimentary record reproduces the original living assemblage, in order to elucidate the potential usefulness of these microorganisms as tracers of past oceanographic/climatic conditions. In addition, a laminated core was examined, and a sequence of thin sections from the Holocene was investigated by backscattered electron imagery. The diatom assemblage in plankton and surface samples is a warm water assemblage typical of oligotrophic waters dominated by nine species: a) A. neocrenulata, Neodelphineis indica and Nitzschia bicapitata in the plank-ton; b) Alveus marinus, Azpeitia neocrenulata, A. nodulifer and Roperia tesselata in surface sediments; c) Actinocyclus curvatulus, resting spores of Chaetoceros spp., N. bicapitata and Thalassionema nitzschioides var. parva within the brine sediments. When comparing plankton and sediment assemblages it becomes obvious that fragile species like N. bicapitata are easily dissolved in the water column and/or at the sedi-ment/water interface, leaving the sediment enriched in robust taxa. However, within the brine sediments these fragile forms are better preserved than in non-brine sediments. Thus, brine sediments in this region offer a great potential for palaeoenvironmental studies. Within the Holocene section of the laminated core from the Shaban Deep, alternating light and dark layers containing coccoliths and terrigenous material (light) and diatom frustules (mainly Rhizosolenia spp., but also Chaetoceros spp.) (dark). These layers can be interpreted as the result of an annual cycle with diatoms representing the spring signal, and coccoliths and the terrigenous debris corresponding to the autumn or early winter signal.
ABSTRACT Sediment in the deep center of the Santa Barbara Basin (SBB) is almost completely lamina... more ABSTRACT Sediment in the deep center of the Santa Barbara Basin (SBB) is almost completely laminated for the portion representing the past ∼2000 years and has been utilized as an archive for high-resolution paleoceanography since the 1970s. Unequivocal proof of the presence of varves in SBB sediment throughout the 20th century has been uncritically used to assume that deeper laminations are varves as well and that they can be counted down-core to arrive at a reliable varve chronology for the past ∼2000 years. The advent of radiocarbon accelerator mass-spectrometric (AMS) dating of sub-milligram-sized organic terrigenous plant fragments and charcoal enabled us to independently date SBB sediment without the underlying uncertainty of variable marine radiocarbon reservoir ages. It was determined that the traditional SBB varve-count ages remain valid from the present down to ∼1700 AD, whereas not all deeper laminations represent varves. Depending on depth, the newly revised chronostratigraphy deviates from the traditional varve count by up to ∼400 years. Here, we present (i) a historic overview of the SBB varve chronology, (ii) a critique of the extended, traditional “varve chronology” and (iii) the rationale behind our new chronology that overcomes the long-standing misunderstanding and bias in lamination counting that was assumed to be “varve counting” below the ∼1700 AD level. Evidence from other California offshore locations indicates that the oxygenation of the deeper water column has been decreasing over the past few hundred years, and this facilitated a transition from laminated and possibly intermittently varved sediment to continuously varved sediment in the SBB.
Geological Society, London, Special Publications, 1996
Abstract: The varved marine anoxic sediment in the deep centre of the Santa Barbara Basin off Cal... more Abstract: The varved marine anoxic sediment in the deep centre of the Santa Barbara Basin off California has been studied extensively by sedimentologists, micropalaeontologists and geochemists during the past four decades. The Santa Barbara Basin is the only basin in the California ...
The Antarctic Circumpolar Current (ACC) is the world's largest current system connecting all ... more The Antarctic Circumpolar Current (ACC) is the world's largest current system connecting all three major basins of the global ocean. Our knowledge of glacial‐interglacial changes in ACC dynamics in the southeast Pacific is not well constrained and presently only based on reconstructions covering the last glacial cycle. Here we use a combination of mean sortable silt grain size of the terrigenous sediment fraction (10–63 μm, ) and X‐ray fluorescence scanner‐derived Zr/Rb ratios as flow strength proxies to examine ACC variations at the Pacific entrance to the Drake Passage (DP) in the vicinity of the Subantarctic Front. Our results indicate that at the DP entrance, ACC strength varied by ~6–16% on glacial‐interglacial time scales, yielding higher current speeds during interglacial times and reduced current speeds during glacials. We provide evidence that previous observations of a reduction in DP throughflow during the last glacial period are part of a consistent pattern extending...
Fjord sediments are increasingly used as high-resolution archives of climate and environmental ch... more Fjord sediments are increasingly used as high-resolution archives of climate and environmental change, including variations in glacier mass balance and terrestrial hydrology. To accurately interpret such sediment records, it is crucial to comprehend sediment transport processes and determine sediment provenance. With this in mind, our main objective is to identify cost-effective parameters that can be used to reconstruct relative variations in the origin of sediments deposited in the Baker-Martínez fjord system, which is located between the Northern (NPI) and Southern (SPI) Patagonian Icefields. We focus on estimating the proportions of sediment derived from each icefield, taking advantage of the clearly distinct lithologies that underlie NPI (Patagonian Batholith) and SPI (Eastern Andean Metamorphic Complex) glaciers. The magnetic susceptibility and inorganic geochemistry of 21 surface sediment samples collected along the fjord system and that of suspended sediment samples from the...
Carbon Cycling in the Glacial Ocean: Constraints on the Ocean’s Role in Global Change, 1994
There are three fundamentally different proxies recording ocean productivity in sediments: those ... more There are three fundamentally different proxies recording ocean productivity in sediments: those representing flux (that is, export production), those representing nutrient concentrations (e.g., nitrate or phosphate), and those representing aspects of the trophic structure of the pelagic environment. Flux proxies disagree due to different power-law relationships to the source term. The particular power-laws (expressed in terms of proxy exponents) change as a function of geography, and may change as a function of time. Modification of the accumulation rate by changing preservation on the sea floor (and within the sediment) is an important aspect of this problem.
ABSTRACT The Red Sea is an oligotrophic water body with special characteristics due to its enclos... more ABSTRACT The Red Sea is an oligotrophic water body with special characteristics due to its enclosed position. There is almost no rainfall, no permanent rivers flowing into the Red Sea, and evaporation is high especially during winter. Phytoplankton is scarce in the oligotrophic Red Sea and dominated by small cells. There is no information on siliceous microorganisms preserved in the sediments of the Red Sea. Here we compare siliceous assemblages (mainly diatoms) from plankton tows and sediments collected along a N-S profile (28^o to 21^oN), and from the Shaban Deep, a brine-filled basin in the central axis of the Red Sea. The goal is to assess the effects of preservation and the accuracy with which the sedimentary record reproduces the original living assemblage, in order to elucidate the potential usefulness of these microorganisms as tracers of past oceanographic/climatic conditions. In addition, a laminated core was examined, and a sequence of thin sections from the Holocene was investigated by backscattered electron imagery. The diatom assemblage in plankton and surface samples is a warm water assemblage typical of oligotrophic waters dominated by nine species: a) A. neocrenulata, Neodelphineis indica and Nitzschia bicapitata in the plank-ton; b) Alveus marinus, Azpeitia neocrenulata, A. nodulifer and Roperia tesselata in surface sediments; c) Actinocyclus curvatulus, resting spores of Chaetoceros spp., N. bicapitata and Thalassionema nitzschioides var. parva within the brine sediments. When comparing plankton and sediment assemblages it becomes obvious that fragile species like N. bicapitata are easily dissolved in the water column and/or at the sedi-ment/water interface, leaving the sediment enriched in robust taxa. However, within the brine sediments these fragile forms are better preserved than in non-brine sediments. Thus, brine sediments in this region offer a great potential for palaeoenvironmental studies. Within the Holocene section of the laminated core from the Shaban Deep, alternating light and dark layers containing coccoliths and terrigenous material (light) and diatom frustules (mainly Rhizosolenia spp., but also Chaetoceros spp.) (dark). These layers can be interpreted as the result of an annual cycle with diatoms representing the spring signal, and coccoliths and the terrigenous debris corresponding to the autumn or early winter signal.
ABSTRACT Sediment in the deep center of the Santa Barbara Basin (SBB) is almost completely lamina... more ABSTRACT Sediment in the deep center of the Santa Barbara Basin (SBB) is almost completely laminated for the portion representing the past ∼2000 years and has been utilized as an archive for high-resolution paleoceanography since the 1970s. Unequivocal proof of the presence of varves in SBB sediment throughout the 20th century has been uncritically used to assume that deeper laminations are varves as well and that they can be counted down-core to arrive at a reliable varve chronology for the past ∼2000 years. The advent of radiocarbon accelerator mass-spectrometric (AMS) dating of sub-milligram-sized organic terrigenous plant fragments and charcoal enabled us to independently date SBB sediment without the underlying uncertainty of variable marine radiocarbon reservoir ages. It was determined that the traditional SBB varve-count ages remain valid from the present down to ∼1700 AD, whereas not all deeper laminations represent varves. Depending on depth, the newly revised chronostratigraphy deviates from the traditional varve count by up to ∼400 years. Here, we present (i) a historic overview of the SBB varve chronology, (ii) a critique of the extended, traditional “varve chronology” and (iii) the rationale behind our new chronology that overcomes the long-standing misunderstanding and bias in lamination counting that was assumed to be “varve counting” below the ∼1700 AD level. Evidence from other California offshore locations indicates that the oxygenation of the deeper water column has been decreasing over the past few hundred years, and this facilitated a transition from laminated and possibly intermittently varved sediment to continuously varved sediment in the SBB.
Geological Society, London, Special Publications, 1996
Abstract: The varved marine anoxic sediment in the deep centre of the Santa Barbara Basin off Cal... more Abstract: The varved marine anoxic sediment in the deep centre of the Santa Barbara Basin off California has been studied extensively by sedimentologists, micropalaeontologists and geochemists during the past four decades. The Santa Barbara Basin is the only basin in the California ...
The Antarctic Circumpolar Current (ACC) is the world's largest current system connecting all ... more The Antarctic Circumpolar Current (ACC) is the world's largest current system connecting all three major basins of the global ocean. Our knowledge of glacial‐interglacial changes in ACC dynamics in the southeast Pacific is not well constrained and presently only based on reconstructions covering the last glacial cycle. Here we use a combination of mean sortable silt grain size of the terrigenous sediment fraction (10–63 μm, ) and X‐ray fluorescence scanner‐derived Zr/Rb ratios as flow strength proxies to examine ACC variations at the Pacific entrance to the Drake Passage (DP) in the vicinity of the Subantarctic Front. Our results indicate that at the DP entrance, ACC strength varied by ~6–16% on glacial‐interglacial time scales, yielding higher current speeds during interglacial times and reduced current speeds during glacials. We provide evidence that previous observations of a reduction in DP throughflow during the last glacial period are part of a consistent pattern extending...
Uploads
Papers by Carina Lange