Understanding Full-Depth Steric Sea Level Change in the Southwest Pacific Basin using Deep Argo

Using nine years of full-depth profiles from 55 Deep Argo floats in the Southwest Pacific Basin collected between 2014 and 2023, we find consistent warm anomalies compared to a long-term climatology below 2000 m ranging between 11 <m:math xmlns:m="http://www.w3.org/1998/Math/MathML" alttext="±" display="inline"><m:mo>±</m:mo></m:math> 2 to 34 <m:math xmlns:m="http://www.w3.org/1998/Math/MathML" alttext="±" display="inline"><m:mo>±</m:mo></m:math> 2m <m:math xmlns:m="http://www.w3.org/1998/Math/MathML" alttext="{}ᵒ" display="inline"><m:msup><m:mi/><m:mi>o</m:mi></m:msup></m:math> C, most pronounced between 3500 and 5000 m. Over this period, a cooling trend is found between 2000-4000 m and a significant warming trend below 4000 m with a maximum rate of 4.1 <m:math xmlns:m="http://www.w3.org/1998/Math/MathML" alttext="±" display="inline"><m:mo>±</m:mo></m:math> 0.31 m <m:math xmlns:m="http://www.w3.org/1998/Math/MathML" alttext="{}ᵒ" display="inline"><m:msup><m:mi/><m:mi>o</m:mi></m:msup></m:math> C yr <m:math xmlns:m="http://www.w3.org/1998/Math/MathML" alttext="{}⁻¹" display="inline"><m:msup><m:mi/><m:mrow><m:mo>-</m:mo><m:mn>1</m:mn></m:mrow></m:msup></m:math> near 5000 m, with a possible acceleration over the second half of the period. The integrated Steric Sea Level expansion below 2000 m was 7.9 <m:math xmlns:m="http://www.w3.org/1998/Math/MathML" alttext="±" display="inline"><m:mo>±</m:mo></m:math> 1 mm compared to the climatology with a trend of 1.3 <m:math xmlns:m="http://www.w3.org/1998/Math/MathML" alttext="±" display="inline"><m:mo>±</m:mo></m:math> 1.6 mm dec <m:math xmlns:m="http://www.w3.org/1998/Math/MathML" alttext="{}⁻¹" display="inline"><m:msup><m:mi/><m:mrow><m:mo>-</m:mo><m:mn>1</m:mn></m:mrow></m:msup></m:math> over the Deep Argo era, contributing significantly to the local sea level budget. We assess the ability to close a full Sea Level Budget, further demonstrating the value of a full-depth Argo array.