A lot of us in the geoscience business are concerned these days with interpreting ongoing and past, and predicting future, responses of landforms, soils, and ecosystems to climate change. As one of my interests is rivers, I have noted over the years that in a lot of the literature on paleohydrology the major changes, such as major influxes of sediment, seem to occur at climate transitions, rather than after climate changes or shifts have had a chance to settle in and exert their impacts for awhile.

A related issue is the relationship between precipitation, temperature, runoff, erosion, and vegetation. As climate changes both temperature and precipitation regimes change. And as every physical geography student knows, moisture availability is not just about precipitation, but the balance between precipitation and evapotranspiration (ET). So, if both temperature and precipitation are increasing (as is the case on average on much of the planet now), whether available moisture increases or decreases depends on the relative increases of precipitation and ET.  

Soil erosion on cropland.

This is a continuation of my earlier post on applying state-and-transition models (STM) to stratigraphic information, to account for the missing bits.

Barrell’s (1917) explanation of how oscillatory variations in base level control the timing of deposition. Sedimentation can only occur when base level is actively rising. These short intervals are indicated by the black bars in the top diagram. The resulting stratigraphic column, shown at the left, is full of disconformities, but appears to be the result of continuous sedimentation. Noted sedimentologist Andrew Miall has used this example in several articles to illustrate the problems of gaps in sedimentary & stratigraphic records.

The reconstruction of past environmental change is more important than ever. First, we look for precedents, principles, and lessons from the past as we try to understand and predict ongoing and future environmental change based on the fundamental wisdom that “if it did happen, it can happen.” Second, all kinds of new ideas on the coevolution of life, landforms, climate, and Earth itself need testing, verification—and maybe most importantly—hypothesis generation from the historical record.

The most important historical records for all but the past couple of centuries are stratigraphic. Environmental change is recorded in the sedimentary rock record, in geologically modern sedimentary deposits, and in soil layers. However, geoscientists have long realized that the stratigraphic record is incomplete—“more gap than record,” Derek Ager famously pointed out, with the preserved events equally famously termed “frozen accidents.” The current state of affairs is well summarized in and recently published volume titled Strata and Time: Probing the Gaps in Our Understanding (Smith et al., 2015).

Wolfgang Scwhanghart, Tobias Heckmann and I have collaborated recently to review applications of graph theory in geomorphology and the geosciences in general. One of our papers, Graph Theory in the Geosciences, was just published in Earth-Science Reviews. The abstract is below. Our other joint paper, dealing specifically with graph theory applications in geomorphology, is still in press (in the journal Geomorphology) even though it was completed and accepted before the ESR paper. Go figure. 

What is the relationship between the diversity of resources (e.g., space, sunlight, water, nutrients) and biodiversity? In most cases it is direct and positive—that is, the greater the diversity of resources the greater the biodiversity.  The relationship is also often mutually reinforcing—that is, byproducts, detritus, and the organisms themselves increase the diversity of the resource base. Of course, ultimately both resource and biodiversity are limited by both abiotic and biotic controls. The relationships look something like this: