Question

why has the temperature of the artic ocean changed during the last 40? less snow falls in the artic now than 40 years ago, sea ice has produced more salt causing the cold ocean water to sink, sea ice has melted allowing more sunlight to hit the ocean, more sunlight now reaches earth than in the past

Answer 1

Short answer: the biggest reasons are greenhouse‑gas warming plus loss of sea ice and snow (which lets the ocean absorb more sunlight). The other choices you listed are either incomplete or incorrect as primary causes.

Quick rundown of each item you mentioned
- "Sea ice has melted allowing more sunlight to hit the ocean" — True and important. When ice and snow disappear they no longer reflect sunlight (albedo), so the dark ocean absorbs more solar energy. That warms the surface and drives a strong positive feedback (Arctic amplification).
- "More sunlight now reaches Earth than in the past" — Not in the sense of the Sun getting brighter. Total solar output has not shown a long‑term increase large enough to explain Arctic warming. What has changed is how much sunlight is absorbed locally at the surface because of lost ice/snow (and in some cases cloud changes).
- "Less snow falls in the Arctic now than 40 years ago" — Not a simple yes. Precipitation patterns have shifted; in many Arctic regions annual precipitation (including snow) has increased because warmer air holds more moisture. What has changed more clearly is snow cover duration and extent (snow melts earlier), which reduces surface albedo and contributes to warming.
- "Sea ice has produced more salt causing the cold ocean water to sink" — Brine rejection during ice formation does make dense water locally, but over recent decades overall summer sea ice has declined and the surface ocean in many places has actually freshened from meltwater and river input. Brine rejection is not the main cause of the long‑term Arctic surface warming.

Other important contributors
- Increased greenhouse gases — raise downward longwave radiation and warm the Arctic atmosphere and ocean.
- Ocean heat transport — more warm Atlantic/Pacific water flowing into Arctic regions (especially the Atlantic sector) brings extra heat.
- Atmospheric changes and feedbacks — changes in clouds, water vapor, and soot (black carbon on snow) also affect regional heating.

If you want sources: look at the IPCC reports (polar chapter), NOAA’s Arctic Report Card, and AMAP assessments — they summarize observations and causes of Arctic warming.