Terrestrial biosphere changes over the last 120 kyr

Abstract

Abstract. A new global synthesis and biomization of long (> 40 kyr) pollen-data records is presented and used with simulations from the HadCM3 and FAMOUS climate models and the BIOME4 vegetation model to analyse the dynamics of the global terrestrial biosphere and carbon storage over the last glacial–interglacial cycle. Simulated biome distributions using BIOME4 driven by HadCM3 and FAMOUS at the global scale over time generally agree well with those inferred from pollen data. Global average areas of grassland and dry shrubland, desert, and tundra biomes show large-scale increases during the Last Glacial Maximum, between ca. 64 and 74 ka BP and cool substages of Marine Isotope Stage 5, at the expense of the tropical forest, warm-temperate forest, and temperate forest biomes. These changes are reflected in BIOME4 simulations of global net primary productivity, showing good agreement between the two models. Such changes are likely to affect terrestrial carbon storage, which in turn influences the stable carbon isotopic composition of seawater as terrestrial carbon is depleted in 13C.

Deglacial carbon cycle changes observed in a compilation of 127 benthic <i>δ</i><sup>13</sup>C time series (20–6 ka)

“…The two y axes are scaled to illustrate the similarity in the pattern of change across the deglaciation but are not meant to imply that the magnitude of change is equivalent. 2 ka and net primary productivity increased from 8-2 ka (Hoogakker et al, 2016). This is consistent with our observation that the global mean benthic δ 13 C trend continued until at least 6 ka.…”

“…The deglacial pattern of global mean ocean δ 13 C change is a proxy for changes in the size of the terrestrial biosphere. If so, global mean δ 13 C should continue to increase after atmospheric CO 2 levels plateau at 11 ka due to the slower response times for ice sheet retreat and ecosystem change (e.g., Hoogakker et al, 2016;DaviesBarnard et al, 2017). We compare the reconstructed global mean δ 13 C change with several carbon cycle model estimates of terrestrial biosphere change.…”

Quantifying the influence of the terrestrial biosphere on glacial–interglacial climate dynamics

“…Australia has a tendency to be too wet in HadCM3 in the present day and hence the coupled model has too much vegetation in this region). However, during glacial times there is a decrease in biomass, consistent with Hoogakker et al (2016).…”

“…This is supported by pollen and other data Anhuf et al, 2006;Wang et al, 2017) and modelling (Cowling et al, 2001) which find that although there is diminished tropical forest, there is still substantial tree cover at the LGM and little sign of widespread grasslands. Conversely, the BIOME6000 data find that the tropical rainforest area was reduced during the LGM (Pickett et al, 2004;Prentice and Jolly, 2000;Bigelow et al, 2003;Harrison et al, 2001) and grasslands expanded, as do some modelling studies (Martin Calvo and Prentice, 2015;Prentice et al, 2011;Hoogakker et al, 2016). It is interesting to note that in the present-day Amazon, BIOME6000 shows three points of tropical forest, two of savanna, two of warm-temperature forest, two of temperate forest, and three of dry grass/shrubland at the LGM.…”

Ocean carbon cycling during the past 130 000 years – a pilot study on inverse palaeoclimate record modelling

“…We do not explicitly model the terrestrial carbon cycle in our experiment. Rather, we assume here that the land biosphere would have a smaller net primary production (Hoogakker et al, 2016) and standing biomass stock and hence provide a release of carbon to the atmosphere under colder and drier conditions. The amplitude for biomass carbon loss from the land biosphere to the atmosphere was set to −1000 Pg C, in line with estimates from terrestrial palaeoclimate records according to Crowley (1995).…”