Icebergs not the trigger for North Atlantic cold events.

Area of Science:

• Paleoclimatology
• Climate Dynamics
• Oceanography

Background:

• Late Pleistocene climate featured abrupt changes, including Dansgaard-Oeschger events, characterized by shifts between warm interstadial and cold stadial conditions.
• These events, recorded in Greenland ice cores, are often linked to alterations in Atlantic Ocean overturning circulation.
• North Atlantic cold events correlate with increased iceberg calving, prompting climate modeling studies using freshwater forcing.

Observation:

• Previous research noted a lag between North Atlantic cooling and ice-rafted debris (IRD) during the last glacial cycle.
• This study confirms a systematic delay between surface cooling and IRD arrival southwest of Iceland over four glacial cycles.
• Comparisons of IRD and polar planktonic foraminifera data were used to establish this temporal relationship.

Findings:

• Icebergs arrived too late to have initiated the observed cooling events.
• Abrupt stadial transitions are likely a nonlinear response to gradual North Atlantic cooling.
• Freshwater from melting icebergs may amplify or extend stadial conditions but does not trigger them.

Implications:

• Revises the causal link between iceberg discharge and abrupt climate change in the North Atlantic.
• Suggests gradual cooling is a primary driver, with iceberg meltwater acting as a feedback mechanism.
• Enhances understanding of the complex dynamics governing Pleistocene abrupt climate variability.