Paleoclimatology and Proxy Records

Greetings to all!

            Paleoclimatology is the study of ancient climates. We obviously don’t have high-resolution data from 10 or 100 million years ago because we didn’t exist! Today we have satellite measurements, meters, gauges, sensors, etc. which give us a very vivid, clear, detailed picture of our reality. But when we look back into deep time, we must gather data through proxy records. Proxy records are “physical, chemical and biological materials preserved within the geologic record” (https://www2.usgs.gov/landresources/lcs/paleoclimate/proxies.asp) and these materials contain pertinent information about events that took millions (or tens of millions) of years to unfold. Today, we will barely scratch the surface.

            We more or less understand tree rings, right? Trees grow outward, year after year. The more rings, the older the tree. The light rings are summer growth, and the dark lines are winter growth. Thicker summer rings indicate favorable growing conditions with sufficient water, light, and nutrients. Thin rings indicate poor growing conditions.

            Now let’s take that a step further. Plants and trees have preferred climatic conditions and they release pollen to reproduce. This pollen wafts on the wind to various destinations and becomes part of the geologic record. Scientists can analyze the relative abundance of certain species over others to determine an approximate temperature and precipitation regime for the area. With error bars, of course as 100% certainty is never guaranteed. Plant macrofossils can also be used in a similar manner to reconstruct past plant assemblages and infer their preferred climate conditions.

Ice cores also offer us glimpses into ancient atmospheres by trapping tiny pockets of air. Glaciers form via the accumulation and compaction of snow, and some ice cores have visible layers much like tree rings. Air trapped in the pore spaces between snowflakes eventually become bubbles trapped in the ice. Scientists use the amount of methane and carbon dioxide to determine a range of likely temperatures based on our observations and understanding of atmospheric chemistry and climate sensitivity. The Vostok ice core contains 400,000 years’ worth of atmospheric data, and it clearly shows how much of an outlier our current CO2 concentration actually is. (http://www.antarcticglaciers.org/glaciers-and-climate/ice-cores/ice-core-basics/).

            Then there are sediment records. Scientists can use the texture, color, structure, density, and magnetic properties of sediments to determine where the sediment came from, where it was likely deposited, which direction wind or water was flowing, how much chlorophyll or rust is present (and therefore what the oxygen conditions were like and how much biological activity occurred), and many other helpful bits of information. Now is a good time to brush up on that chemistry refresher article explaining what isotopes are! And might as well review the slow carbon cycle article, too. Their respective links are below. http://www.trinityjournal.com/community/columnists/article_e52b01a4-0529-11ec-bd09-c720e79ed003.html http://www.trinityjournal.com/community/clubs_and_organizations/article_4471c402-102b-11ec-9805-176802389de5.html

Plankton are microscopic organisms in the ocean that form calcium carbonate shells. The oxygen in these shells can either be O16 or O18, meaning it can either contain 8 neutrons, or 10 neutrons, respectively.

(8 protons + 8 neutrons = an atomic weight of 16)

(8 protons + 10 neutrons = an atomic weight of 18)

            O16 is preferentially evaporated, meaning it becomes gaseous before the heavier O18 does. In periods of extensive glaciation when continental ice sheets are at their thickest, we clearly see more O16 in the ice core records and, here’s the kicker, more O18 in the calcium carbonate shells in ocean sediments! More O18 in the ocean means bigger glaciers. More O16 in the ocean means significantly less glaciation. Coral reefs also create calcium carbonate skeletons and they grow outward and form growth layers, also similar to trees. Proxy records can be used for comparison and calibration as we refine our estimates. There are always more data to discover.

            To those with a knack for chemistry, biology, and geology, proxy records provide rich treasure troves of information about the vast, mysterious, magical world that is our home planet.

            Keep exploring and never stop learning, friends!