Retrieving data from an Arduino SD card module with a Raspberry Pi?

I’m working on a project that will require both an Arduino and a Raspberry Pi.
The Arduino (a Mega 2560) will be responsible for recording sensor data to an SD card.
The RPi will boot once an hour to perform photography tasks involving a DSLR, manipulate the image data, and uploading images and sensor data to a server. The RPi will not be powered full time so as to conserve battery capacity. (Solar setup)

I’m struggling with finding an elegant way to have the RPi be able to access, download, and interact (delete) data on the Arduino SD card. I am open to any reasonable suggestions. The data on the card that needs to be downloaded each hour will consist primarily of a CSV text file containing the sensor data. There will also be sporadic instances of JPG files that need to be copied from the Arduino (motion activated cameras).

I’m leaning toward Ethernet as the common interconnect, but the power requirements of the various Ethernet modules is a bit much to stomach. I’m experimenting with powering off (with a relay) the Arduino Ethernet module when not needed.

Any help would be appreciated.

This is a communication problem but you make no mention of the most important criterion - the distance between the parties. If they are reasonably close, say 30m, bluetooth low-energy would have to be a hell of a lot easier on the power supply than a grossly under-employed ethernet system.

Irrespective of the means, all that is required is for Arduino to make files named after date and hour, and Raspberry Pi to send the name to Arduino to retrieve the file. Thie latter is a standard file dump procedure.

As for deleting the files, I guess the first thing you need to do is come up with a reason for doing that, then consider if getting a bigger card is in fact a better solution.