Direct observations of ice seasonality reveal changes in climate over the past 320-570 years.

Sapna Sharma,Yasuyuki Aono,Ryan D Batt,Luke A Winslow,Johanna Korhonen,John J Magnuson

doi:10.1038/srep25061

Abstract

Lake and river ice seasonality (dates of ice freeze and breakup) responds sensitively to climatic change and variability. We analyzed climate-related changes using direct human observations of ice freeze dates (1443–2014) for Lake Suwa, Japan, and of ice breakup dates (1693–2013) for Torne River, Finland. We found a rich array of changes in ice seasonality of two inland waters from geographically distant regions: namely a shift towards later ice formation for Suwa and earlier spring melt for Torne, increasing frequencies of years with warm extremes, changing inter-annual variability, waning of dominant inter-decadal quasi-periodic dynamics, and stronger correlations of ice seasonality with atmospheric CO2 concentration and air temperature after the start of the Industrial Revolution. Although local factors, including human population growth, land use change, and water management influence Suwa and Torne, the general patterns of ice seasonality are similar for both systems, suggesting that global processes including climate change and variability are driving the long-term changes in ice seasonality.

Highlights

After the start of the Industrial Revolution: i) Do ice dates reveal more rapid warming? ii) Do warm extremes increase in frequency? iii) Does inter-annual variability increase? iv) Do frequencies of quasi-periodic dynamics change? and v) Do drivers of ice seasonality change?
Both Suwa and Torne exhibited more rapid rates of change consistent with warming with later ice freeze and earlier ice breakup following the start of the Industrial Revolution (Fig. 1)
The trend in ice breakup date for Torne decreased from − 0.30 days per decade before the breakpoint (1693–1866) to − 0.66 days per decade after the breakpoint (1867–2013; more negative values indicate earlier ice breakup; Fig. 1B)

Summary

Introduction

The record for the date of ice breakup for Torne River, defined as when the ice was generally moving, was started by a merchant named Olof Ahlbom in 1693. Torne is a northern river flowing southward into the Baltic Sea from the Arctic. It is one of the largest unregulated rivers in Scandinavia with a length of 522 kilometers and a watershed basin of 40,145 square kilometres. The river flows through a forested valley and two small towns, Haparanda, Sweden, and Tornio, Finland, populated by 15,000 people[19,20]. The extent and annual grain of the Suwa and Torne ice records allowed us to address how climate and variability differed before and after the start of the Industrial Revolution. After the start of the Industrial Revolution: i) Do ice dates reveal more rapid warming? ii) Do warm extremes increase in frequency? iii) Does inter-annual variability increase? iv) Do frequencies of quasi-periodic dynamics (i.e., oscillations of periods with different lengths) change? and v) Do drivers (i.e., explanatory factors) of ice seasonality change?

Methods

Results

Conclusion