How Robust Is the Apparent Break‐Down of Northern High‐Latitude Temperature Control on Spring Carbon Uptake?

Abstract

• No significant change in the overall temperature sensitivity of high northern latitude spring greenness in the past 40 years • Decreased spatial coherence of spring temperature anomalies has increased the influence of atmospheric transport on surface CO2 data • Temperature sensitivity of spring carbon uptake remains strong when accounting for atmospheric transport Accepted Article This article has been accepted for publication and undergone full peer review but has not been through the copyediting, typesetting, pagination and proofreading process, which may lead to differences between this version and the Version of Record. Please cite this article as

Temperature dependence of spring carbon uptake in northern high latitudes during the past four decades

“…Our factorial experiments indicate a minor influence of atmospheric transport compared to NBP in controlling the SZC and SCC variations at Barrow (Figure 3), contrary to a previous study (Joyce et al., 2021) based on a different model. This reflects uncertainties in both terrestrial biosphere models and atmosphere transport models that need to be better constrained in future studies.…”

“…This reflects uncertainties in both terrestrial biosphere models and atmosphere transport models that need to be better constrained in future studies. Nonetheless, the declined spatial synchrony of T Mar–Jun anomalies during the middle period could enlarge the role of the year to year varying atmospheric transport (Joyce et al., 2021), acting in synergy for the ostensible dip of the temperature dependence of SZC and SCC.…”

“…(2017) inferred that the strong temperature control on spring carbon uptake before the late 1990s has weakened during 1996–2012. There are, however, contradictory evidences, including a whole ecosystem warming experiment for boreal woody species that showed an unbroken linear response of spring phenology to the increased temperatures up to +9°C (Richardson et al., 2018), and a modeling work that indicated a major role of variations in atmospheric circulation rather than in spring NBP that could explain the weakened apparent temperature sensitivity at Barrow site (Joyce et al., 2021). Thus, whether the strength of temperature control on spring carbon uptake has changed during the past decades, and the mechanisms underlying such change if it does occur, remain elusive.…”

Warming response of peatland CO2 sink is sensitive to seasonality in warming trends

“…Contemporary NEE observations or short-term manipulation experiments (<10 years) probably cannot capture these slow changes 51 . Similar to peatlands, other boreal and temperate ecosystems have been found to experience increased net CO 2 uptake in response to warmer spring and early-growing-season temperatures and decreased uptake with warming in the late growing season and the related reductions in water availability and enhanced water stress [52][53][54][55][56][57][58] . In addition, atmospheric CO 2 concentration records have shown that since the late 1990s peak growing season, net CO 2 uptake across northern latitudes is increasing with warmer air temperatures in the region 59 .…”