scholarly journals Evidence of Changes in Sedimentation Rate and Sediment Fabric in a Low Oxygen Setting: Santa Monica Basin, CA

2019 ◽  
Author(s):  
Nathaniel Kemnitz ◽  
William Berelson ◽  
Douglas Hammond ◽  
Laura Morine ◽  
Maria Figueroa ◽  
...  
Keyword(s):  
Accumulation Rate ◽  
Laminated Sediments ◽  
Accumulation Rates ◽  
Low Oxygen ◽  
The Past ◽  
Santa Monica ◽  
Santa Monica Basin ◽  
Sedimentary Dynamics ◽  
Sediment Fabric ◽  
Mass Accumulation Rates

Abstract. The Southern California Bight is adjacent to one of the world's largest urban areas, Los Angeles. As a consequence, anthropogenic impacts could disrupt local marine ecosystems due to municipal and industrial waste, pollution, and flood control measures. Superimposed on the growth of an urban metropolis, the impact of climate change has been felt most strongly over the past 50 years in terms of rising pCO2 and warming. Santa Monica Basin (SMB), due to its unique setting in low oxygen and high sedimentation environment, has provided an excellent sedimentary paleorecord of these anthropogenic changes. This study examined ten sediment cores, collected from different parts of the SMB between spring and summer 2016, and compared them to existing cores in order to document changes in sedimentary dynamics during the last 250 years, with an emphasis on the last 40 years. Mass accumulation rates (MAR) for the deepest and lowest oxygen-containing parts of the SMB basin (900–910 m) established using 210Pb have been remarkably consistent during the past century, averaging 17.5 ± 2.1 mg/cm2-yr. At slightly shallower sites (870–900 m), accumulation rates showed more variation, butyield the same accumulation rate, 17.5 ± 5.5 mg/cm2-yr. Excess 210Pb sedimentation rates were consistent with rates established using bomb-test 137Cs profiles. However, 14C profiles from cores collected in the deepest part of the SMB, where fine laminations are present up to 250 years B.P., indicate that MAR was slower prior to ~ 1900 CE (rates obtained = 9 and 12 mg/cm2-yr). δ13Corg profiles show a relatively constant value down core suggesting that the change in sediment accumulation rate is not accompanied by a change in organic carbon sources to the basin. The increase in sedimentation rate towards the recent occurs at about the time previous studiespredicted an increase in siltation and the demise of a shelly shelf benthic fauna on the SMB shelf. X-radiographs show finely laminated sediments in the deepest part of the basin only, with cm-scale layering of sediments or no layering whatsoever in shallower parts of the SMB basin. The absence of finely laminated sediments in MUC 10 (893 m) and MUC 3 (777 m) suggest that the rate at which anoxia is spreading, has not increased appreciably since cores were last analyzed in the 1980s. Based on core top data collected during the past half century, sedimentary dynamics within SMB has changed minimally during last 40 years. Specifically, mass accumulation rates, laminated sediment fabric, extent of bioturbation, and % Corg have not changed. The only parameter that appeared to have changed in the last 250 years was the MAR with an apparent step-wise increase occurring between ~ 1850–1900 CE, yet the post-1900 CE constancy of sedimentation through a period of massive urbanization is surprising.

scholarly journals Evidence of changes in sedimentation rate and sediment fabric in a low-oxygen setting: Santa Monica Basin, CA

2020 ◽  
Vol 17 (8) ◽  
pp. 2381-2396
Author(s):  
Nathaniel Kemnitz ◽  
William M. Berelson ◽  
Douglas E. Hammond ◽  
Laura Morine ◽  
Maria Figueroa ◽  
...  
Keyword(s):  
Los Angeles ◽  
Accumulation Rate ◽  
Laminated Sediments ◽  
Accumulation Rates ◽  
Low Oxygen ◽  
The Past ◽  
Santa Monica ◽  
Santa Monica Basin ◽  
Sedimentary Dynamics ◽  
Sediment Fabric

Abstract. The Southern California Bight is adjacent to one of the world's largest urban areas, Los Angeles. As a consequence, anthropogenic impacts could disrupt local marine ecosystems due to municipal and industrial waste discharge, pollution, flood control measures, and global warming. Santa Monica Basin (SMB), due to its unique setting in a low-oxygen and high-sedimentation environment, can provide an excellent sedimentary paleorecord of these anthropogenic changes. This study examined 10 sediment cores, collected from different parts of the SMB between spring and summer 2016, and compared them to existing cores in order to document changes in sedimentary dynamics during the last 250 years, with an emphasis on the last 40 years. The 210Pb-based mass accumulation rates (MARs) for the deepest and lowest oxygen-containing parts of the SMB basin (900–910 m) have been remarkably consistent during the past century, averaging 17.1±0.6 mg cm−2 yr−1. At slightly shallower sites (870–900 m), accumulation rates showed more variation but yield the same accumulation rate, 17.9±1.9 mg cm−2 yr−1. Excess 210Pb sedimentation rates were consistent with rates established using bomb test 137Cs profiles. We also examined 14C profiles from two cores collected in the deepest part of the SMB, where fine laminations are present up to about 450 yr BP. These data indicate that the MAR was slower prior to ∼1900 CE (rates obtained were 9 and 12 mg cm−2 yr−1). The δ13Corg profiles show a relatively constant value where laminations are present, suggesting that the change in sediment accumulation rate is not accompanied by a change in organic carbon sources to the basin. The increase in sedimentation rate towards the Recent occurs at about the time previous studies predicted an increase in siltation and the demise of a shelly shelf benthic fauna on the SMB shelf. X-radiographs show finely laminated sediments in the deepest part of the basin only, with centimeter-scale layering of sediments or no layering whatsoever in shallower parts of the SMB basin. The absence of finely laminated sediments in cores MUC 10 (893 m) and MUC 3 (777 m) suggests that the rate at which anoxia is spreading has not increased appreciably since cores were last analyzed in the 1980s. Based on core top data collected during the past half century, sedimentary dynamics within SMB have changed minimally during the last 40 years. Specifically, mass accumulation rates, laminated sediment fabric, extent of bioturbation and % Corg have not changed. The only parameter that appeared to have changed in the last 450 years was the MAR, with an apparent > 50 % increase occurring between ∼1850 CE and the early 1900s. The post-1900 CE constancy of sedimentation through a period of massive urbanization in Los Angeles is surprising.

Geochemical and sedimentologic variations in inter-annually laminated sediments from Santa Monica Basin

1995 ◽  
Vol 125 (1-2) ◽  
pp. 111-131 ◽  
Author(s):  
James W. Hagadorn ◽  
Lowell D. Stott ◽  
Ashish Sinha ◽  
Miguel Rincon
Keyword(s):  
Laminated Sediments ◽  
Santa Monica ◽  
Santa Monica Basin ◽  
Annually Laminated Sediments

Cladocera Community Response to Experimental Eutrophication in Lake 227 as Recorded in Laminated Sediments

1994 ◽  
Vol 51 (10) ◽  
pp. 2312-2321 ◽  
Author(s):  
Brenda J. Hann ◽  
Peter R. Leavitt ◽  
Philip S. S. Chang
Keyword(s):  
Standing Crop ◽  
Accumulation Rate ◽  
Sediment Accumulation ◽  
Community Response ◽  
Laminated Sediments ◽  
Accumulation Rates ◽  
Experimental Lakes Area ◽  
Northwestern Ontario ◽  
Annually Laminated Sediments ◽  
Chemical Conditions

The response of pelagic zooplankton to experimental fertilization was compared with the fossil record of Cladocera obtained from the annually laminated sediments of Lake 227, Experimental Lakes Area, northwestern Ontario. Constrained cluster analysis of both total fossil Cladocera and littoral chydorid communities clearly distinguished between pre- and post-eutrophication communities and further differentiated between years of high and low nitrogen:phosphorus fertilization ratios. However, there were few chydorid species extirpations resulting from the manipulation. Total chydorid accumulation rates and indices of species diversity, richness, and equitability were relatively constant over the last century and were not affected by fertilization. Among pelagic Cladocera, Bosmina longirostris abundance declined > 60% after initial fertilization. Although harsh chemical conditions (pH > 10) may have contributed to reduced abundance of pelagic Cladocera, Bosmina populations were also naturally variable prior to manipulation. Changes in Bosmina morphology (mucrone, antennule, and carapace length) and cladoceran size ratios (Daphnia/[Daphnia + Bosmina]) suggested that zooplanktivory by fish and invertebrates exercised important control of herbivore populations. Fossil Bosmina concentration (remains∙[g dry wt]−1 or remains∙[g organic matter]−1) were significantly correlated (r = 0.66, P < 0.01, 1970–1989) to standing crop in the water column (animals∙m−2). Fossil accumulation rate (remains∙cm−2∙yr−1) was not significantly correlated to Bosmina abundance, perhaps because of errors in determining bulk sediment accumulation rates.

scholarly journals PRELIMINARY STUDY OF SEDIMENT AGES AND ACCUMULATION RATES IN JAKARTA BAY DERIVED FROM DEPTH PROFILES OF UNSUPPORTED 210Pb

2010 ◽  
Vol 6 (3) ◽  
pp. 256-260
Author(s):  
Ali Arman Lubis ◽  
Barokah Aliyanta
Keyword(s):  
Accumulation Rate ◽  
Sediment Accumulation ◽  
Accumulation Rates ◽  
The Past ◽  
Unsupported 210Pb ◽  
Scuba Divers ◽  
Decay Series ◽  
238U Decay Series ◽  
Pips Detector ◽  
Preliminary Study

Preliminary study of sediment ages and accumulation rates has been carried out in Jakarta Bay using unsupported 210Pb. 210Pb occurs naturally in sediments as one of the radioisotopes in the 238U decay series. The total 210Pb activity in sediments has two components, namely; supported and unsupported. The latter derives from dissociation of 210Pb from 226Ra through diffusion of the intermediate gaseous isotope 222Rn which diffuse into the atmosphere and decay to 210Pb. 210Pb falling directly into seawater and deposit on the bed of the marine with sediments. 210Pb has half-life of 22.26 years makes it well suited to dating and determining the accumulation rate of sediments laid down over the past 100 - 150 years. Two cores samples with diameter 7.5 cm were taken by scuba divers from Jakarta Bay and were analyzed of 210Pb using α-spectrometer equipped with PIPS detector. The sediment ages and range of sediment accumulation rates of core I and II are up to 169 years and (0.25 - 1.93) kg/m2y and up to 157 years and (0.15 - 2.68) kg/m2y, respectively.  Keywords: sediment ages, accumulation rates, marine sediment, 210Pb

scholarly journals Recent precipitation decrease across the western Greenland ice sheet percolation zone

2019 ◽  
Vol 13 (11) ◽  
pp. 2797-2815 ◽  
Author(s):  
Gabriel Lewis ◽  
Erich Osterberg ◽  
Robert Hawley ◽  
Hans Peter Marshall ◽  
Tate Meehan ◽  
...  
Keyword(s):  
Mass Loss ◽  
Mass Balance ◽  
Accumulation Rate ◽  
Ice Sheet ◽  
Greenland Ice Sheet ◽  
Snow Accumulation ◽  
Accumulation Rates ◽  
The Past ◽  
Precipitation Decrease ◽  
Percolation Zone

Abstract. The mass balance of the Greenland Ice Sheet (GrIS) in a warming climate is of critical interest in the context of future sea level rise. Increased melting in the GrIS percolation zone due to atmospheric warming over the past several decades has led to increased mass loss at lower elevations. Previous studies have hypothesized that this warming is accompanied by a precipitation increase, as would be expected from the Clausius–Clapeyron relationship, compensating for some of the melt-induced mass loss throughout the western GrIS. This study tests that hypothesis by calculating snow accumulation rates and trends across the western GrIS percolation zone, providing new accumulation rate estimates in regions with sparse in situ data or data that do not span the recent accelerating surface melt. We present accumulation records from sixteen 22–32 m long firn cores and 4436 km of ground-penetrating radar, covering the past 20–60 years of accumulation, collected across the western GrIS percolation zone as part of the Greenland Traverse for Accumulation and Climate Studies (GreenTrACS) project. Trends from both radar and firn cores, as well as commonly used regional climate models, show decreasing accumulation rates of 2.4±1.5 % a−1 over the 1996–2016 period, which we attribute to shifting storm tracks related to stronger atmospheric summer blocking over Greenland. Changes in atmospheric circulation over the past 20 years, specifically anomalously strong summertime blocking, have reduced GrIS surface mass balance through both an increase in surface melting and a decrease in accumulation rates.

scholarly journals Investigating the past and recent δ<sup>18</sup>O-accumulation relationship seen in Greenland ice cores

2012 ◽  
Vol 8 (6) ◽  
pp. 2053-2059 ◽  
Author(s):  
S. L. Buchardt ◽  
H. B. Clausen ◽  
B. M. Vinther ◽  
D. Dahl-Jensen
Keyword(s):  
Temperature Rise ◽  
Accumulation Rate ◽  
Ice Core ◽  
Ice Cores ◽  
Accumulation Rates ◽  
Data Set ◽  
The Past

Abstract. Decadal means of δ18O and accumulation rates from 52 ice core locations in Greenland are presented. The accumulation rates are derived from annual layers determined in the δ18O curve. Investigation of the δ18O-accumulation relationship across the ice divide reveals a significant Foehn effect with anticorrelation of δ18O and accumulation rate on the lee side of the divide in Southern Greenland, while no effect is seen in Central Greenland. Furthermore, the sensitivity of accumulation rate to changes in temperature is found to be smaller in Northern Greenland than in the central and southern parts. Four records in the data set contain sufficient recent data that the period of observed temperature rise from the 1990s and onwards can be investigated. All four records are from locations close to the ice divide in Northern Greenland and while three of them show increased temperatures, no conclusive statement can be made about the accumulation rate from these data.

Non-annual laminations and expansion of anoxic basin-floor conditions in Santa Monica Basin, California Borderland, over the past four centuries

1994 ◽  
Vol 116 (3-4) ◽  
pp. 399-418 ◽  
Author(s):  
Christopher J Christensen ◽  
Donn S Gorsline ◽  
Douglas E Hammond ◽  
Steven P Lund
Keyword(s):  
The Past ◽  
California Borderland ◽  
Santa Monica ◽  
Santa Monica Basin ◽  
Anoxic Basin ◽  
Basin Floor

scholarly journals Variations in export production, lithogenic sediment transport and iron fertilization in the Pacific sector of the Drake Passage over the past 400 ka

2021 ◽  
Author(s):  
María H. Toyos ◽  
Gisela Winckler ◽  
Helge W. Arz ◽  
Lester Lembke-Jene ◽  
Carina B. Lange ◽  
...  
Keyword(s):  
Southern Ocean ◽  
Drake Passage ◽  
Accumulation Rates ◽  
Export Production ◽  
The Core ◽  
The Past ◽  
Iron Fertilization ◽  
The Pacific ◽  
Mass Accumulation Rates ◽  
Mass Accumulation

Abstract. Changes in Southern Ocean export production have broad biogeochemical and climatic implications. Specifically, iron fertilization likely increased subantarctic nutrient utilization and enhanced the efficiency of the biological pump during glacials. However, past export production in the subantarctic Southeast Pacific is poorly documented, and its connection to Fe fertilization, potentially related to Patagonian Ice Sheet dynamics is unknown. We report on biological productivity changes over the past 400 ka, based on a combination of 230Thxs-normalized and stratigraphy-based mass accumulation rates of biogenic barium, organic carbon, biogenic opal, and calcium carbonate as indicators of paleo-export production in a sediment core upstream of the Drake Passage. In addition, we use fluxes of iron and lithogenic material as proxies for terrigenous matter, and thus potential micronutrient supply. Stratigraphy-based mass accumulation rates are strongly influenced by bottom-current dynamics, which result in variable sediment focussing or winnowing at our site. Carbonate is virtually absent in the core, except during peak interglacial intervals of the Holocene, and Marine Isotope Stages (MIS) 5 and 11, likely caused by transient decreases in carbonate dissolution. All other proxies suggest that export production increased during most glacial periods, coinciding with high iron fluxes. Such augmented glacial iron fluxes at the core site were most likely derived from glaciogenic input from the Patagonian Ice Sheet promoting the growth of phytoplankton. Additionally, glacial export production peaks are also consistent with northward shifts of the Subantarctic and Polar Fronts, which positioned our site south of the Subantarctic Front and closer to silicic acid-rich waters of the Polar Frontal Zone, as well as a with a decrease in the diatom utilization of Si relative to nitrate under Fe-replete conditions. However, glacial export production near the Drake Passage was lower than in the Atlantic and Indian sectors of the Southern Ocean, which may relate to complete consumption of silicic acid in the study area. Our results underline the importance of micro-nutrient fertilization through lateral terrigenous input from South America rather than aeolian transport, and exemplify the role of frontal shifts and nutrient limitation for past productivity changes in the Pacific entrance to the Drake Passage.

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