by Lynn Fichter (James Madison Univ.)5 Figure 1.2 is a sketch of terrestrial (land) and marine (ocean) depositional environments (i.e., environments where sediments are deposited). These include the settings of the paleoclimate archives shown in Figure 1.1. In which of these setting(s) (A‐E3) would you expect to find relatively uninterrupted accumulation (or growth for biological archives)? Explain your answer.Examine the photos of a sedimentary rock outcrop, an ocean sediment core, and an ice core (Figure 1.3). These could have originated from locations E1, E3, and C respectively in the block diagram (Figure 1.2).FIGURE 1.3. Three paleoclimate archives. (a) A sedimentary outcrop from Bastrop, TX.(Source: photo courtesy of John Firth, IODP). (b) An ice core segment, ~9 cm wide (photo by Janine and Jim Eden, Flickr Creative Commons license as posted to https://www.dnr.wa.gov/programs‐and‐services/geology/glaciers#the‐cordilleran‐ice‐sheet.1.).(c) An ocean sediment core segment, ~7 cm wide; it was originally a cylinder that was cut in half lengthwise (from IODP, http://www.iodp.tamu.edu/publications 199_IR/chap_13/chap_13.htm).
6 How are the sedimentary rock outcrop and ocean sediment core similar? How are they different?
7 How are the ice core and the ocean sediment core similar? How are they different?The quality of the paleoclimate record is also affected by what has happened to the archive since the initial recording (i.e., since the time when the archive was first formed or deposited). For example, as sediments can be lithified into sedimentary rock; rocks and sediments and the fossils they contain can be weathered and eroded; ice can melt; and organic matter can decay. All of these processes can degrade the information recorded and, therefore, increase uncertainty about the data and its interpretation. These processes also affect the maximum time range that an archive spans and therefore the time interval for which it is useful for paleoclimate reconstructions.The various types of proxy data must be described and interpreted by those who have learned how to “read” natural archives. This typically involves making observations and measurements using a wide range of analytical equipment (e.g. hand lens, microscopes, gas chromatographs, mass spectrometers). While we rely on the various proxy data to reconstruct paleoclimates, it is important to also recognize that each analytical method has its own limitations which can influence resolution, maximum time ranges, and scientific uncertainty.Examine the data in Table 1.1 which summarize the typical (although exceptions certainly exist!) spatial and temporal distribution of each of the paleoclimate archives in Figure 1.1. Also included in Table 1.1 are examples of the proxy data and climate parameters that can be reconstructed from these archives. Additional resources on each of these archives can be found in the supplementary materials associated with this book. In Table 1.1 notice that lake sediments, marine sediments, and sedimentary rocks, while all sedimentary sequences, are displayed in separate rows in this table because of their distinctly different timeframes and temporal and spatial (geographic) resolutions (Figure 1.4).TABLE 1.1. Selected major paleoclimate archives and the proxy data they contain.Adapted from Cronin (1999) Principles of Paleoclimatology, with information from Ruddiman (2008) Earth's Climate Past and Future, http://www.ncdc.noaa.gov/paleo, http://www.ngdc.noaa.gov/mgg/curator/curator.html, and https://www.ncei.noaa.gov.https://www.sciencemag.org/news/2017/08/record‐shattering‐27‐Myr‐old‐ice‐core‐reveals‐start‐ice‐agesArchiveGeographic Distribution & Number of Sites: Where are these records typically found? How many records have been collected? (see also Figure 1.4a,b)Time Range: How far back in time can we typically go? (years before present)Temporal Resolution: How detailed can we typically get? (years)Types of Proxy Data: What is typically measured and analyzed?Past Climate Conditions: What climatic information can the proxy data typically tell us about?ContinentalTree ringsGlobal, but most sites in the Northern Hemisphere; >6000 sites~10 000<1Cellulose; stable and radioactive isotopes; Ring widthsSeasonal precipitation; fires; and temperature; ageLake sedimentsGlobal, but most sites in the Northern Hemisphere; ~100 s of sites<1 000 0001–20Microfossils and pollen types and abundances; paleomagnetic patterns; stable and radioactive isotopes; trace elements; alkenone biomarkers; sediment composition and geochemistryRegional changes in precipitation and evaporation; temperature; salinity; volcanic activity; glacial activity; erosion rates; chemical weathering; ageSpeleothems (cave deposits)Global; >50 sites<500 0001–2000Stable and radioactive isotopes; trace elementsTemperature; precipitation, atmospheric CO2; ageIce sheets and glaciersPolar ice sheets, and high altitude (alpine) temperate and tropical glaciers; >80 sites<2 700 000<1–1000Stable and radioactive isotopes; trace elements; dust and other particulates; atmospheric gas concentrationsTemperature; precipitation; wind/atmospheric circulation; atmospheric chemistry including CO2; volcanic activity; biomass burning; ageSedimentary rocksGlobal; 10 s of thousands of sites<3 600 000 00010 000–100 000Microfossil and pollen types and abundances; paleomagnetic patterns; sediment composition; stable and radioactive isotopes; depositional patternsTemperature; biological productivity; volcanic activity; glacial activity; sea level; ice volume; evolution; chemical weathering; ageOceanicCoralsTropical and subtropical oceans, >60 sites<650 000<1–1000Growth bands; stable and radioactive isotopes; trace elementsSalinity; temperature; nutrients; sea level; ice volume; ageMarine sedimentsGlobal; >65 000 sites<200 000 000100–10 000Microfossil and pollen types and abundances; paleomagnetic patterns; stable and radioactive isotopes; trace elements; alkenone biomarkers; sediment composition; depositional patternsOcean and atmospheric circulation; temperature; salinity; nutrients; aridity on land; biological productivity; volcanic activity; glacial activity; ice volume; chemical weathering; age FIGURE 1.4. (a) Global geographic distribution of lake and ocean core sites. Different colors represent different ships (platforms). From National Centers for Environmental Information NOAA, https://maps.ngdc.noaa.gov/viewers/sample_index. (b) Global geographic distribution of sample locations for tree ring records (green triangles), coral records (yellow circles), ice cores (blue triangles), and speleothem records (gray circles). From National Centers for Environmental Information NOAA, https://gis.ncdc.noaa.gov/maps/ncei/paleo?layers=0000000000000001
8 The oldest sediments in the modern ocean are ~200 million years (Myr) old. How would we learn about ocean conditions prior to 200 million years ago?
9 Based on Table 1.1 and Figure 1.4a,b:Which archives have the widest geographic distribution and the greatest number of sites sampled?Which archives have the fewest sites sampled?
10 Where are there “gaps” in the geographic distribution of paleoclimate records? In other words, where has sampling been sparse?
11 Imagine there are two paleoclimate records both covering the last 500 000 yr, but
