7.7 Marine sediment records
9 min read•august 21, 2024
Marine sediments are time capsules of Earth's past, preserving crucial information about ocean conditions and global climate changes. By studying different types of sediments and analyzing their isotope systems, scientists can reconstruct ancient environments and understand long-term Earth processes.
Various paleoclimate proxies in marine sediments allow researchers to piece together past sea temperatures, ocean circulation patterns, and productivity levels. Dating techniques and careful core analysis help create accurate timelines, enabling scientists to track glacial cycles, ocean acidification, and methane release events throughout Earth's history.
Types of marine sediments
- Marine sediments provide crucial information about past ocean conditions and global climate changes
- Studying different types of marine sediments allows geochemists to reconstruct paleoenvironments and understand long-term Earth system processes
- Isotope analysis of marine sediments forms the foundation for many paleoceanographic and paleoclimatic studies
Biogenic vs terrigenous sediments
Top images from around the web for Biogenic vs terrigenous sediments
12.6 Sediment Distribution – Introduction to Oceanography View original
Is this image relevant?
Putting It Together: Rocks and the Rock Cycle | Geology View original
Is this image relevant?
Putting It Together: Rocks and the Rock Cycle | Geology View original
Is this image relevant?
12.6 Sediment Distribution – Introduction to Oceanography View original
Is this image relevant?
Putting It Together: Rocks and the Rock Cycle | Geology View original
Is this image relevant?
1 of 3
Top images from around the web for Biogenic vs terrigenous sediments
12.6 Sediment Distribution – Introduction to Oceanography View original
Is this image relevant?
Putting It Together: Rocks and the Rock Cycle | Geology View original
Is this image relevant?
Putting It Together: Rocks and the Rock Cycle | Geology View original
Is this image relevant?
12.6 Sediment Distribution – Introduction to Oceanography View original
Is this image relevant?
Putting It Together: Rocks and the Rock Cycle | Geology View original
Is this image relevant?
1 of 3
- Biogenic sediments originate from marine organisms (plankton shells, coral skeletons)
- Terrigenous sediments derive from land-based sources (river discharge, wind-blown dust)
- Biogenic sediments dominate in open ocean areas far from land
- Terrigenous sediments concentrate near continental margins and in regions with high dust input
- Ratio of biogenic to terrigenous sediments indicates changes in ocean productivity and terrestrial weathering rates
Carbonate vs siliceous sediments
- Carbonate sediments consist primarily of calcium carbonate (CaCO3) from marine organisms (foraminifera, coccolithophores)
- Siliceous sediments composed of opaline silica (SiO2 • nH2O) from diatoms and radiolarians
- Carbonate sediments dominate in tropical and temperate regions above the lysocline
- Siliceous sediments prevalent in high-latitude and upwelling regions with high nutrient content
- Carbonate-to-silica ratio in sediments reflects changes in ocean chemistry and biological productivity
Deep-sea vs coastal sediments
- Deep-sea sediments accumulate slowly in low-energy environments (1-5 cm per 1000 years)
- Coastal sediments deposit rapidly in high-energy settings (up to several meters per 1000 years)
- Deep-sea sediments provide long, continuous records of global climate changes
- Coastal sediments offer high-resolution information on local environmental conditions
- Comparing deep-sea and coastal records helps reconstruct past sea-level changes and ocean circulation patterns
Isotope systems in sediments
- Isotope systems in marine sediments serve as powerful tools for reconstructing past environmental conditions
- Different isotope systems provide unique insights into various aspects of the ocean-climate system
- Combining multiple isotope proxies allows for a more comprehensive understanding of past oceanic and climatic changes
Oxygen isotopes in foraminifera
- Oxygen isotope ratios (18O/16O) in foraminiferal shells reflect seawater temperature and global ice volume
- values increase during glacial periods due to preferential 16O storage in ice sheets
- Species-specific vital effects influence oxygen isotope fractionation in foraminifera
- Benthic foraminifera provide information on deep ocean temperatures and ice volume
- Planktonic foraminifera record sea surface temperatures and local salinity variations
Carbon isotopes in organic matter
- Carbon isotope ratios (13C/12C) in sedimentary organic matter indicate changes in marine productivity
- Higher values suggest increased primary production and carbon burial
- Terrestrial vs marine organic matter sources have distinct carbon isotope signatures
- Carbon isotopes in organic matter help reconstruct past ocean nutrient cycling
- Changes in atmospheric CO2 levels can be inferred from long-term carbon isotope records
Strontium isotopes in carbonates
- Strontium isotope ratios () in marine carbonates reflect global weathering rates
- Seawater 87Sr/86Sr increases during periods of enhanced continental weathering
- Strontium isotopes provide information on long-term climate and tectonic changes
- Marine carbonate 87Sr/86Sr values are uniform globally due to long oceanic residence time of Sr
- Strontium isotope stratigraphy used for dating and correlating marine sediments
Neodymium isotopes in ferromanganese crusts
- Neodymium isotope ratios () in ferromanganese crusts trace ocean circulation patterns
- εNd values vary between ocean basins due to different continental inputs
- Changes in εNd over time reflect shifts in ocean circulation and weathering sources
- Ferromanganese crusts provide long-term records of ocean chemistry (millions of years)
- Neodymium isotopes help reconstruct past ocean overturning circulation strength
Paleoclimate proxies
- Paleoclimate proxies in marine sediments allow scientists to reconstruct past environmental conditions
- Multiple proxies are often combined to provide a comprehensive view of past climate states
- Calibration of proxies using modern observations and laboratory experiments is crucial for accurate interpretations
Sea surface temperature reconstruction
- in planktonic foraminifera shells indicate past sea surface temperatures
- (UK'37) derived from coccolithophore biomarkers reflects growth temperature
- based on archaeal membrane lipids provides sea surface temperature estimates
- Oxygen isotopes in coral skeletons record sea surface temperature and salinity changes
- Combining multiple temperature proxies improves the accuracy of paleoclimate reconstructions
Ocean circulation patterns
- Carbon isotope gradients between benthic foraminifera from different ocean basins trace deep water masses
- Neodymium isotopes in ferromanganese crusts and fish teeth indicate changes in water mass provenance
- Protactinium/Thorium (Pa/Th) ratios in sediments reflect changes in Atlantic Meridional Overturning Circulation strength
- Sortable silt mean size serves as a proxy for bottom current speed
- Radiocarbon age differences between surface and deep-water indicate ocean ventilation rates
Productivity and nutrient cycling
- Barium excess in sediments (Ba excess) indicates changes in export productivity
- Nitrogen isotopes () in organic matter reflect nutrient utilization and nitrogen fixation
- Cadmium/Calcium (Cd/Ca) ratios in foraminifera shells record changes in phosphate concentrations
- Biogenic opal accumulation rates indicate siliceous productivity changes
- in sediments reflect organic carbon burial and bottom water oxygenation
Sea level changes
- Oxygen isotopes in benthic foraminifera provide estimates of global ice volume and sea level
- Coral reef terraces record past sea level highstands
- Sedimentary facies changes in continental shelf deposits indicate transgression and regression events
- Foraminiferal transfer functions based on species assemblages estimate past water depths
- Combining multiple sea level proxies improves the accuracy of paleoshoreline reconstructions
Sediment dating techniques
- Accurate dating of marine sediments is crucial for establishing chronologies and correlation between records
- Different dating techniques are applicable to various time scales and sediment types
- Combining multiple dating methods helps improve age model reliability
Radiocarbon dating
- Radiocarbon (14C) dating applicable to organic materials up to ~50,000 years old
- Marine reservoir effect correction needed for ocean-derived carbon
- Calibration curves convert radiocarbon ages to calendar years
- Accelerator (AMS) allows dating of small samples (foraminifera)
- used for constructing age models in late Quaternary sediment cores
U-series dating
- Uranium-series dating based on decay of uranium isotopes to thorium
- 230Th dating applicable to carbonates (corals) up to ~500,000 years old
- 231Pa/230Th dating used for estimating sedimentation rates and ocean circulation changes
- U-series disequilibrium in sediments indicates diagenetic processes
- Combining U-series with other dating methods improves age constraints on older sediments
Biostratigraphy
- Biostratigraphy uses fossil assemblages to determine relative ages of sediments
- First and last appearance datums (FADs and LADs) of species define biostratigraphic zones
- Microfossil biostratigraphy (foraminifera, nannofossils) widely used in marine sediments
- Magnetostratigraphy often combined with biostratigraphy for improved age control
- Biostratigraphic dating crucial for sediments beyond the range of radiometric techniques
Sediment core analysis
- analysis involves various techniques to extract paleoenvironmental information
- Proper core sampling and preparation are essential for accurate geochemical measurements
- Advances in analytical techniques have improved the precision and resolution of sediment core data
Core sampling and preparation
- Sediment cores obtained using gravity corers, piston corers, or drilling platforms
- Core sections carefully split, described, and photographed
- Sampling intervals determined based on research objectives and core resolution
- Samples dried, weighed, and disaggregated for various analyses
- Microfossils extracted through wet sieving and picking under microscope
Stable isotope mass spectrometry
- Isotope ratio mass spectrometry (IRMS) measures stable isotope ratios in sediment components
- Sample preparation involves acid digestion for carbonates or combustion for organic matter
- Dual inlet systems provide high precision for δ18O and δ13C measurements
- Continuous flow IRMS allows for rapid, automated analysis of large sample sets
- Internal and external standards used to ensure measurement accuracy and precision
Trace element analysis
- Inductively Coupled Plasma Mass Spectrometry (ICP-MS) measures trace element concentrations
- Laser Ablation ICP-MS enables high-resolution analysis of individual microfossils
- X-ray Fluorescence (XRF) core scanning provides non-destructive elemental profiles
- Trace element ratios (Mg/Ca, Sr/Ca) used as paleoenvironmental proxies
- Calibration using matrix-matched standards ensures accurate quantification
Paleoceanographic applications
- Marine sediment records provide insights into past ocean conditions and global climate changes
- Paleoceanographic studies help understand natural climate variability and predict future changes
- Integration of multiple proxy records allows for comprehensive reconstructions of past ocean-climate states
Glacial-interglacial cycles
- Marine sediments record cyclical changes in global ice volume and ocean circulation
- Oxygen isotope records from benthic foraminifera show ~100,000-year glacial cycles
- Carbon isotope changes reflect reorganizations of the global carbon cycle during glacial-interglacial transitions
- Trace element proxies indicate changes in ocean temperature and productivity between glacial and interglacial periods
- Sediment composition changes (carbonate vs silica) reflect shifts in ocean chemistry and circulation patterns
Ocean acidification records
- (δ11B) in foraminifera shells record past seawater pH changes
- Trace element ratios (U/Ca, B/Ca) in carbonates indicate changes in ocean carbonate chemistry
- Carbonate preservation indices reflect past changes in lysocline depth and carbonate saturation state
- Combining multiple proxies allows reconstruction of past pCO2 levels and ocean acidification events
- Paleocene-Eocene Thermal Maximum (PETM) serves as an analog for modern anthropogenic ocean acidification
Methane hydrate release events
- Carbon isotope excursions in sedimentary records indicate past methane releases
- Hydrogen index and organic matter δ13C used to identify methane-derived carbon inputs
- Benthic foraminiferal extinctions associated with methane hydrate destabilization events
- Barium concentrations in sediments reflect changes in methane-fueled productivity
- Clathrate gun hypothesis links methane hydrate releases to rapid climate warming events
Challenges and limitations
- Understanding the limitations of marine sediment records is crucial for accurate paleoenvironmental interpretations
- Researchers must consider various factors that can affect the fidelity of sedimentary archives
- Ongoing research aims to improve proxy calibrations and develop new techniques to address these challenges
Bioturbation and diagenesis
- Bioturbation by benthic organisms can mix sediments and smooth high-resolution signals
- Diagenetic processes alter original geochemical signatures in sediments over time
- Authigenic mineral formation can overprint primary isotopic and elemental compositions
- Selective dissolution of carbonate shells can bias foraminiferal assemblages and isotope records
- Careful sample selection and multi-proxy approaches help mitigate bioturbation and diagenetic effects
Spatial and temporal resolution
- Sedimentation rates vary widely between different ocean regions and depositional environments
- Low sedimentation rates in deep-sea settings limit the temporal resolution of paleoclimate records
- Spatial coverage of sediment cores is uneven, with gaps in important oceanic regions
- Interpolation between widely spaced data points can introduce uncertainties in global reconstructions
- Development of new coring techniques and identification of high-resolution sites improve temporal and spatial coverage
Proxy calibration uncertainties
- Modern calibrations may not fully capture the range of past environmental conditions
- Species-specific vital effects can complicate the interpretation of geochemical proxies
- Secondary factors (salinity, carbonate ion concentration) can influence proxy relationships
- Calibration uncertainties propagate through paleoenvironmental reconstructions
- Ongoing research in culturing experiments and sediment trap studies aims to refine proxy calibrations
Future directions
- Advancements in analytical techniques and proxy development continue to expand the field of paleoceanography
- Integration of marine sediment records with other paleoclimate archives and climate models improves our understanding of Earth's climate system
- Future research directions focus on addressing current limitations and exploring new avenues for
Novel isotope systems
- Clumped isotope thermometry in carbonates provides absolute temperature estimates
- Silicon and zinc isotopes in diatoms reflect changes in nutrient utilization and ocean pH
- Chromium isotopes in carbonates indicate changes in oceanic redox conditions
- Calcium isotopes in foraminifera shells record variations in the marine calcium cycle
- Development of non-traditional stable isotope systems (Mo, Fe, Cu) for tracing ocean biogeochemical cycles
High-resolution records
- Identification and coring of high sedimentation rate sites (drift deposits, coastal sediments)
- Development of microsampling techniques for analyzing individual foraminifera chambers
- Application of scanning techniques (XRF core scanning, hyperspectral imaging) for ultra-high resolution records
- Annually laminated sediments (varves) provide seasonal to interannual climate information
- Combination of high-resolution sediment records with annually resolved archives (corals, speleothems)
Integration with climate models
- Data-model comparisons improve understanding of climate forcings and feedbacks
- Assimilation of proxy data into climate models enhances paleoclimate reconstructions
- Forward modeling of proxy systems helps refine interpretations of sedimentary records
- Ensemble modeling approaches quantify uncertainties in paleoclimate reconstructions
- Integration of marine sediment data with ice core, terrestrial, and model results provides a comprehensive view of past climate states
Key Terms to Review (28)
143Nd/144Nd: The ratio of neodymium isotopes 143Nd to 144Nd is a crucial measurement in isotope geochemistry, often used to trace geological processes and sources of sediments. This ratio helps to understand the age and origin of marine sediments, revealing information about past oceanic conditions and continental weathering. Variations in this ratio can indicate changes in sediment provenance and help reconstruct historical climate events.
87Sr/86Sr: 87Sr/86Sr is the ratio of strontium isotopes used as a geochemical tracer to understand various geological and environmental processes. This ratio is particularly important in studying marine sediment records, as it provides insights into past seawater compositions and the sources of sediment, reflecting changes in the Earth's crust and hydrosphere over time.
Alkenone Unsaturation Index: The alkenone unsaturation index is a proxy measurement used in paleoclimatology to estimate historical sea surface temperatures based on the ratio of specific alkenones produced by marine phytoplankton. By analyzing the unsaturation levels of these alkenones, scientists can infer temperature changes over geological timescales, connecting this information to marine sediment records that capture long-term climate variations.
Authigenic uranium concentrations: Authigenic uranium concentrations refer to the uranium that is formed in place within marine sediments through various geochemical processes, such as diagenesis and precipitation. These concentrations are important for understanding the biogeochemical cycles of uranium and can serve as indicators of past environmental conditions in marine settings, often reflecting changes in oxygen levels and organic matter content.
Benthic Sediment: Benthic sediment refers to the material that settles on the seabed, primarily composed of particles such as sand, silt, clay, and organic matter. This sediment serves as a crucial record of past marine environments and biological activity, providing valuable insights into historical climate conditions and oceanographic processes.
Biogenic Fractionation: Biogenic fractionation refers to the preferential uptake or release of isotopes by biological processes, leading to differences in the isotopic composition of materials produced by living organisms compared to those formed through abiotic processes. This phenomenon is essential for understanding past environmental conditions and biological activity, especially in marine sediment records, where the isotopic signatures can reveal insights into historical climate changes and oceanic conditions.
Boron Isotopes: Boron isotopes, primarily $$^{10}B$$ and $$^{11}B$$, are variations of the boron element that have different numbers of neutrons but the same number of protons. These isotopes are crucial in geochemistry and environmental science for tracing processes and understanding past climate conditions, especially through their roles in marine sediment records, interactions with carbon isotopes, and contaminant source identification. Their ratios can provide insights into ocean chemistry, paleoclimatic conditions, and sources of pollutants in various ecosystems.
Carbon-13: Carbon-13 is a stable isotope of carbon, comprising about 1.1% of natural carbon, and is characterized by having six protons and seven neutrons. This isotope plays a crucial role in various scientific fields due to its unique properties, including its applications in understanding biological processes, tracing carbon cycles, and analyzing sediment records.
Climate Proxies: Climate proxies are natural recorders of climate variability and change, providing indirect evidence of past climate conditions. These proxies include various geological, biological, and chemical indicators that reflect changes in the Earth's climate over time, allowing scientists to reconstruct historical climate patterns without direct measurements like thermometers or rain gauges.
David A. Hodell: David A. Hodell is a prominent geochemist known for his influential research on marine sediment records and their applications in understanding past climate changes. His work has significantly advanced the field by using isotopic and elemental analyses of marine sediments to reconstruct historical environmental conditions, contributing to our knowledge of global climate dynamics.
Diagenesis: Diagenesis refers to the physical and chemical processes that sediments undergo after deposition and before metamorphism. This term encompasses various transformations, including compaction, cementation, and mineral changes, which affect the original sediment's characteristics. Understanding diagenesis is crucial for interpreting sedimentary records and paleoclimate conditions as it influences the preservation and alteration of isotopic signatures in sediments.
Diatom Biostratigraphy: Diatom biostratigraphy is a scientific method that uses diatoms, a type of microscopic algae, to date and correlate marine sediment layers based on their fossilized remains. This technique helps researchers understand past environmental conditions, climatic changes, and the timing of sediment deposition by analyzing the specific diatom species present in sediment cores. Diatom biostratigraphy plays a vital role in reconstructing oceanographic history and provides insights into how ecosystems have responded to global changes over time.
Foraminifera assemblages: Foraminifera assemblages are groups of single-celled marine organisms characterized by their calcareous shells, or tests, that accumulate in marine sediments over time. These assemblages are important for understanding past ocean conditions, as they reflect changes in environmental factors like temperature, salinity, and nutrient availability, making them valuable indicators in marine sediment records.
G. s. s. w. b. m. r. demenocal: The term g. s. s. w. b. m. r. demenocal refers to the concept of global sea surface water balance and its relationship to marine records, specifically in the context of understanding climate changes through marine sediment data. This concept is crucial for interpreting past oceanic conditions and shifts in climate, as marine sediments can provide valuable insights into historical sea surface temperatures, salinity, and other related parameters that are vital for reconstructing Earth's climatic history.
Mass spectrometry: Mass spectrometry is an analytical technique used to measure the mass-to-charge ratio of ions, enabling the identification and quantification of different isotopes in a sample. This technique is crucial in isotope geochemistry for analyzing stable and radioactive isotopes, understanding decay processes, and determining isotopic ratios in various materials.
Mg/ca ratios: Mg/Ca ratios refer to the ratio of magnesium to calcium in marine carbonates and sediments, often used as a proxy for past ocean temperatures and carbonate chemistry. By analyzing these ratios in marine sediment records, scientists can infer changes in climate and ocean conditions over geological time scales, revealing important patterns in Earth's history.
Nuclear Magnetic Resonance: Nuclear Magnetic Resonance (NMR) is a powerful analytical technique that exploits the magnetic properties of atomic nuclei to provide detailed information about the structure and dynamics of molecules. By applying a strong magnetic field and radiofrequency radiation, NMR enables scientists to analyze isotopic composition and molecular interactions, making it essential in fields such as isotope geochemistry, environmental studies, and contaminant analysis.
Oxygen-18: Oxygen-18 is a stable isotope of oxygen, consisting of eight protons and ten neutrons in its nucleus, making it heavier than the more common oxygen-16. This isotope plays a critical role in various scientific fields, as it helps in understanding processes like climate change, hydrology, and geochemistry due to its unique properties and variations in natural abundance.
Paleoenvironmental reconstruction: Paleoenvironmental reconstruction is the scientific method used to interpret and recreate past environmental conditions based on geological and biological evidence. This process often utilizes isotopic analysis to understand climate changes, ecosystem dynamics, and the geological context in which these environments existed. By examining isotopic compositions and abundances, researchers can infer details about ancient climates, biological activity, and changes over geological time scales.
Pelagic sediment: Pelagic sediment refers to the fine-grained deposits that accumulate on the ocean floor, primarily composed of organic material, mineral particles, and remains of marine organisms. This type of sediment typically settles in deep-sea environments far from land, making it distinct from other sediment types like neritic or coastal sediments. The composition and characteristics of pelagic sediment can provide valuable insights into past oceanic conditions and biological activity, as well as the geological history recorded in marine sediment cores.
Radiocarbon dating: Radiocarbon dating is a scientific method used to determine the age of an object containing organic material by measuring the amount of carbon-14 it contains. This technique is crucial for understanding past environments, climate changes, and the timing of events in archaeology, allowing researchers to connect timelines across various fields such as marine sediment studies, biological processes, and forensic investigations.
Sediment Core: A sediment core is a cylindrical section of sediment that has been extracted from the ocean floor or other sedimentary environments to study past environmental conditions and changes. These cores are crucial for understanding marine sediment records as they contain layered deposits that reflect various geological and biological processes over time, allowing scientists to reconstruct historical climate variations, oceanographic changes, and even human impacts on marine ecosystems.
Tex86 index: The tex86 index is a paleotemperature proxy derived from the relative abundance of specific tetraether lipids, primarily produced by marine Thaumarchaeota, in marine sediments. This index allows scientists to reconstruct historical sea surface temperatures and understand past climate conditions based on sedimentary records, connecting biological processes and temperature variations over geological timescales.
Thermocline mixing: Thermocline mixing refers to the process of vertical mixing in water bodies, specifically within the thermocline layer, where a rapid change in temperature occurs with depth. This mixing is crucial in marine environments as it affects nutrient distribution, oxygen levels, and the overall ecology of the ocean. It plays a significant role in how sediment records are formed and interpreted, as it influences the deposition and preservation of materials that tell us about past marine conditions.
U-Th Dating: U-Th dating, or uranium-thorium dating, is a radiometric dating method that utilizes the decay of uranium isotopes into thorium to determine the age of calcium carbonate materials, such as coral and cave deposits. This technique is particularly useful for dating geological formations and marine sediments, providing insights into past climate changes and sea level fluctuations.
δ13c: δ13c is a stable carbon isotope ratio that expresses the difference in the abundance of the stable carbon isotopes 13C and 12C in a sample compared to a standard. It provides insights into various processes in nature, including biological activity, environmental changes, and geological phenomena. Understanding δ13c is crucial for interpreting stable isotope data in many fields, including paleoclimate studies, pollution tracking, and geochemical processes.
δ15n: The term δ15n refers to the stable nitrogen isotope ratio, specifically the difference in the abundance of the nitrogen isotopes 15N and 14N in a sample compared to a standard. It provides insight into various ecological and biogeochemical processes by tracking nitrogen cycling, sources, and transformations within different environments, including sediments, atmospheric systems, and marine ecosystems.
δ18o: The δ18o value represents the ratio of stable oxygen isotopes, specifically the ratio of ^18O to ^16O, in a sample compared to a standard. It is a critical metric used in geochemistry to understand temperature changes, precipitation patterns, and various geological processes across different environments.