Reconstructing Earth's Climate History. Kristen St. John

the Greenland Ice Sheet at Summit, Greenland (72°N, 38°W). A year later, the U.S. Greenland Ice Sheet Project 2 (GISP2) completed drilling of a companion record through the ice sheet 30 km to the west. What value might there be in obtaining two parallel ice core records so close together?

      5 The upper 2788 m of the GRIP ice core contains a Greenland paleoclimate record of the last 110 000 yr. The European Project for Ice Coring in Antarctica (EPICA) recovered the deepest and oldest ice record to date at Dome C, Antarctica. This 3270.2 m‐long ice core contains a paleoclimate record of the last 740 000 yr.Calculate the average ice accumulation rates (cm/yr) for the GRIP and EPICA ice cores. Show your work, including the conversion from meters to centimeters.Which has a higher average ice accumulation rate: GRIP or EPICA? Circle your answer.Which record spans a greater period of Earth history: GRIP or EPICA? Circle your answer.Which has a higher average resolution: GRIP or EPICA? Explain your reasoning.

      Coring Marine Paleoclimate Archives

      Corals

      Corals are colonial animals that primarily live in clear, shallow, warm waters of the tropical ocean. The animals themselves are small polyps with flower‐like tentacles that move with the currents to catch plankton. Corals also receive nutrients from photosynthetic algae that live within their tissue. Individual coral polyps secrete crystals of aragonite, a form of calcium carbonate (CaCO₃), which makes a hard external skeleton that is shared by the colony. This is like a shared apartment building for thousands of individual coral polyps. The skeletal structure grows as coral polyps build upon the existing structure that earlier generations secreted. Annual growth patterns can be recognized in climate‐related seasonal variations in the density of the skeletal material. These density differences show up easily on X‐ray images of corals (Figure 1.1d).

      The skeletal structure of living and dead corals extends the record of climate change from modern day into prehistorical times, before instrumental observations of ocean conditions such as sea surface temperature were available. Some large living corals contain continuous records of climate and environmental change for the past 500 yr, and fossil corals give glimpses into even older time periods.

      1 Corals are a marine paleoclimate archive, but they share some characteristics with tree ring archives and speleothem archives. Provide at least one similarity for each:Similarity with tree rings:Similarity with speleothems:

      2  Go to the supplemental resources to watch videos and read a short article on the coral coring process. Make a list of the challenges of obtaining coral cores for paleoclimate research and the strategies scientists use to overcome these challenges.ChallengesSolutions

      3 Starfish and worms can attach and burrow through the coral surface. How might this action affect the quality of the paleoclimate record that a coral can provide?

      4 Go to the supplemental resources and read the USGS article on Corals as Climate Indicators. How are the coral cores prepared for sampling once the cores arrive in the lab?

      5 The composition of the skeletal structure of corals can contain trace elements including magnesium, strontium, and barium (Mg, Sr, and Ba, respectively), which substitute for some of the Ca in the chemical formula of aragonite (CaCO3). Studies of modern corals show that the relative proportion of these trace elements to the proportion of Ca depends on the temperature of seawater in which the coral is living.Look at an online periodic table of the elements. Why would it make sense that Mg, Sr, and Ba can substitute for Ca in the aragonite formula? (Hint: what do Ca, Sr, Mg, and Ba all have in common?)What is the value of having coral records that can be linked to contemporaneous instrumental sea surface temperatures?How would such records be useful for deciphering past coral data?

FIGURE 1.8. Scientific research vessel, JOIDES Resolution.

      Source: Credit: William Crawford, IODP/TAMU, http://iodp.tamu.edu/scienceops/gallery/exp321

      Ocean Sediments

The JOIDES Resolution (Figure 1.8) is one of the vessels designed to obtain core from below the seafloor. Use readings and videos in the supplemental resources to learn about scientific ocean drilling. In particular, take a virtual tour of this ship and watch short videos on the coring process.

      1 How are vessels used for scientific ocean drilling specially outfitted to enable them to recover cores from below the seafloor?The map in Figure 1.9 shows all of the drill site locations from the 50+ year history of scientific ocean drilling expeditions. At each of these drill site locations, several holes may have been drilled and tens to hundreds of cores, each planned to be 9.5 m long, recovered. To more easily carry and store the cores, each is cut into 1.5‐m sections (Figures 1.5 and 1.10). The core sections are also split length‐wise into two halves – a working half, which is used in sampling, and an archive half, which is used for nondestructive analyses and for core photography (Figure 1.11). In total, there are currently >40 000 m of core recovered from below the seafloor, and > 2.3 million samples taken of specific cm‐long intervals of the core sections. To keep so many samples organized for scientific research, it is important that each sample has a unique and meaningful identification code.FIGURE 1.9. Scientific ocean drilling site locations of the International Ocean Discovery Program (IODP; 2013–2021) and predecessor programs, the Integrated Ocean Drilling Program (IODP; 2003–2013), the Ocean Drilling Program (ODP; 1928–2003), and the Deep Sea Drilling Project (DSDP; 1968–1983). From: http://iodp.tamu.edu/scienceops/maps.html

      2 Think about marine core samples. How could you ensure a unique identification for each sample so that you knew exactly where in the subseafloor it came from? What are the essential pieces of information needed?FIGURE 1.10. Example of coring and core terminology (from ODP Leg [i.e. Expedition] 199 Initial Reports Volume, Explanatory Notes: http://www‐odp.tamu.edu/publications/199_IR/chap_02/chap_02.htm).

      3  The standard labeling for ocean drilling samples is shown in Figure 1.10.Deconstruct the sample identification “199‐1215A‐2H‐5, 80‐85” by filling in the blanks below:Leg____ Site_____ Hole____ Core____ Section ____ Centimeter interval ________.Place an X on Figure 1.11 marking the location of this sample.Science requires both qualitative skills and quantitative skills. In questions 23–27, you will quantify some of the costs (with respect to time and money) involved in obtaining sediment cores from below the seafloor.

      4 Expedition (Leg) 199 began in Honolulu, Hawaii on 28 October 2001. The JOIDES Resolution left port at 0830 hours on 28 October and transited 1158 km to the first drilling location, Site 1215, arriving at 2100 hours on 30 October 2001. What was the average rate of travel (i.e. speed) during transit in km/hr? Convert this value to miles/hr. Show your work, including conversion.FIGURE 1.11. Photo of the archive‐half of Core 2 from Hole 1215A, located in the central tropical Pacific Ocean. The sections of the